Fall-Applied Row Covers Enhance Yield in Plasticulture Strawberries; Gardening Guidebook for Washington County, North Carolina www.scribd.com/doc/239851313 ~ Master Gardeners, North Carolina State University, For more information, Please see Organic Edible Schoolyards & Gardening with Children www.scribd.com/doc/239851214 - Double Food Production from your School Garden with Organic Tech www.scribd.com/doc/239851079 - Free School Gardening Art Posters www.scribd.com/doc/239851159 - Increase Food Production with Companion Planting in your School Garden www.scribd.com/doc/239851159 - Healthy Foods Dramatically Improves Student Academic Success www.scribd.com/doc/239851348 - City Chickens for your Organic School Garden www.scribd.com/doc/239850440 - Huerto Ecológico, Tecnologías Sostenibles, Agricultura Organica www.scribd.com/doc/239850233 - Simple Square Foot Gardening for Schools, Teacher Guide www.scribd.com/doc/23985111 ~
Fall-Applied Row Covers Enhance Yield in Plasticulture Strawberries; Gardening Guidebook for Washington County, North Carolina www.scribd.com/doc/239851313 ~ Master Gardeners, North Carolina State University, For more information, Please see Organic Edible Schoolyards & Gardening with Children www.scribd.com/doc/239851214 - Double Food Production from your School Garden with Organic Tech www.scribd.com/doc/239851079 - Free School Gardening Art Posters www.scribd.com/doc/239851159 - Increase Food Production with Companion Planting in your School Garden www.scribd.com/doc/239851159 - Healthy Foods Dramatically Improves Student Academic Success www.scribd.com/doc/239851348 - City Chickens for your Organic School Garden www.scribd.com/doc/239850440 - Huerto Ecológico, Tecnologías Sostenibles, Agricultura Organica www.scribd.com/doc/239850233 - Simple Square Foot Gardening for Schools, Teacher Guide www.scribd.com/doc/23985111 ~
Structural diversity and nutrient recycling potentials of three selected agro...Agriculture Journal IJOEAR
Abstract— Homegardens in Kerala mimic forest ecosystems on account of the tree components included and are agroforestry systems that integrate different agricultural crops and enterprises as per the needs and interests of the farm family. Analysis of the structural diversity and nutrient recycling potentials of three agroforestry homegardens in southern Kerala revealed multi-tier cropping patterns with cropping intensities ranging from 177.18 to 187.04%. Two of the homegardens included livestock components adding to the nutritional security of the family. Diversity indices were in the order 0.92, 1.53 and 0.86. The quantum of litter fall varied with the tree canopies and species, amounting to 473.6, 425.37 and 345.11 kg adding 7.02, 7.517 and 5.165 kg NPK annually in the three homegardens. Maximum nutrient additions were recorded for nitrogen and potassium and least for phosphorus.
Impact of climate on seed morphology and plant growth of Caesalpinia bonduc L...Innspub Net
Caesalpinia bonduc L. is an important medicinal plant threatened by overexploitation. In the present study, the
impact of climate on seed morphology, germination capacity, seedling and plant growth of C. bonduc were evaluated. A total of 2000 seeds were collected in Sudanian and Guinean climate zones of Africa and their length, width, thickness, weight and color were recorded. A hierarchical classification and canonical discriminant analysis were applied to the above traits of seeds from the different climatic zones. An analysis of variance with repeated measures was applied to seeds morphotypes identified by the hierarchical classification to test for the effect of these morphotypes on seed germination, seedling and plant growth. Hierarchical classification helped to
identify four seed morphotypes. Canonical discriminant analysis performed on these morphotypes revealed highly significant differences. Morphotypes 1 and 3 comprised green seeds mainly from Sudanian zone while morphotypes 2 and 4 gathered grey seeds mainly from Guinean zone. Morphotype 3 had the longest seeds while the shortest seeds were from morphotype 1. The heaviest seeds were found in morphotype 4 whereas the lightest ones were from morphotype 1. Seeds of morphotype 4 were the thickest and widest, while the slimmest and most narrow ones were grouped in morphotype 1. Moprhotype 3, consisting of large green seeds mainly from Sudanian zone, was superior in terms of seedling and plant growth among all morphotypes and should be the best choice
for planting purposes of the species.
Canopy effect of Prosopis juliflora on selected grass species by using soil a...Open Access Research Paper
Allelopathy effect of Prosopis juliflora canopy soil aqueous extracts on tropical grass species such as Cenchrus cillaris, Paspalidium desertorum and Lintonia nutans were tested under in vitro conditions. Leaf litter falling under canopy soil was collected and tested for allelopathic effects of soil aqueous extract under natural conditions. All the soil aqueous extracts showed significantly negative effects on both germination and seedling growth of test grass species. The results showed that seed germination percentage decreased with increasing the level of the concentration as well as canopy distance. In Cenchrus ciliaris grass species showed 41.64 and 28.56% reduction in seed germination with 5 and 10% soil aqueous extract respectively, in 0 to 3 meter canopy distance. Whereas, at the same concentration level, the seed germination percentage was 57 and 53% in 3 to 10 meter canopy distance. A similar trend of reduction in seed germination percentage was also noticed in Paspalidium desertorum and Lintonia nutans grass species. Moreover, this study revealed that seedling growth such as shoot and root length was significantly affected by canopy soil extracts at the highest concentration. The effect of 0 to 3 meter canopy soil extract was the highest, followed by 3 to 10 meter canopy soil extracts. Moreover, at low concentration canopy, soil aqueous extract showed less inhibitory effect as compared with higher concentration. It can conclude that Prosopis juliflora contains water-soluble allelochemicals capable of inhibiting selected grass species and Prosopis is not good for agro ecosystem and biodiversity.
Structural diversity and nutrient recycling potentials of three selected agro...Agriculture Journal IJOEAR
Abstract— Homegardens in Kerala mimic forest ecosystems on account of the tree components included and are agroforestry systems that integrate different agricultural crops and enterprises as per the needs and interests of the farm family. Analysis of the structural diversity and nutrient recycling potentials of three agroforestry homegardens in southern Kerala revealed multi-tier cropping patterns with cropping intensities ranging from 177.18 to 187.04%. Two of the homegardens included livestock components adding to the nutritional security of the family. Diversity indices were in the order 0.92, 1.53 and 0.86. The quantum of litter fall varied with the tree canopies and species, amounting to 473.6, 425.37 and 345.11 kg adding 7.02, 7.517 and 5.165 kg NPK annually in the three homegardens. Maximum nutrient additions were recorded for nitrogen and potassium and least for phosphorus.
Impact of climate on seed morphology and plant growth of Caesalpinia bonduc L...Innspub Net
Caesalpinia bonduc L. is an important medicinal plant threatened by overexploitation. In the present study, the
impact of climate on seed morphology, germination capacity, seedling and plant growth of C. bonduc were evaluated. A total of 2000 seeds were collected in Sudanian and Guinean climate zones of Africa and their length, width, thickness, weight and color were recorded. A hierarchical classification and canonical discriminant analysis were applied to the above traits of seeds from the different climatic zones. An analysis of variance with repeated measures was applied to seeds morphotypes identified by the hierarchical classification to test for the effect of these morphotypes on seed germination, seedling and plant growth. Hierarchical classification helped to
identify four seed morphotypes. Canonical discriminant analysis performed on these morphotypes revealed highly significant differences. Morphotypes 1 and 3 comprised green seeds mainly from Sudanian zone while morphotypes 2 and 4 gathered grey seeds mainly from Guinean zone. Morphotype 3 had the longest seeds while the shortest seeds were from morphotype 1. The heaviest seeds were found in morphotype 4 whereas the lightest ones were from morphotype 1. Seeds of morphotype 4 were the thickest and widest, while the slimmest and most narrow ones were grouped in morphotype 1. Moprhotype 3, consisting of large green seeds mainly from Sudanian zone, was superior in terms of seedling and plant growth among all morphotypes and should be the best choice
for planting purposes of the species.
Canopy effect of Prosopis juliflora on selected grass species by using soil a...Open Access Research Paper
Allelopathy effect of Prosopis juliflora canopy soil aqueous extracts on tropical grass species such as Cenchrus cillaris, Paspalidium desertorum and Lintonia nutans were tested under in vitro conditions. Leaf litter falling under canopy soil was collected and tested for allelopathic effects of soil aqueous extract under natural conditions. All the soil aqueous extracts showed significantly negative effects on both germination and seedling growth of test grass species. The results showed that seed germination percentage decreased with increasing the level of the concentration as well as canopy distance. In Cenchrus ciliaris grass species showed 41.64 and 28.56% reduction in seed germination with 5 and 10% soil aqueous extract respectively, in 0 to 3 meter canopy distance. Whereas, at the same concentration level, the seed germination percentage was 57 and 53% in 3 to 10 meter canopy distance. A similar trend of reduction in seed germination percentage was also noticed in Paspalidium desertorum and Lintonia nutans grass species. Moreover, this study revealed that seedling growth such as shoot and root length was significantly affected by canopy soil extracts at the highest concentration. The effect of 0 to 3 meter canopy soil extract was the highest, followed by 3 to 10 meter canopy soil extracts. Moreover, at low concentration canopy, soil aqueous extract showed less inhibitory effect as compared with higher concentration. It can conclude that Prosopis juliflora contains water-soluble allelochemicals capable of inhibiting selected grass species and Prosopis is not good for agro ecosystem and biodiversity.
Diversity of Soil Fauna and Ecosystem Function tariqulmasud12
Soils are natural resources of utmost. Importance for a number of ecosystem and biosphere processes such as plant production, cycling of organic matter and nutrients, storage of C and water, and release of nitrous oxides, CO2 and methane. Soil degradation, through various processes, is a matter of great concern, since their integrity is absolutely critical to increasing food production (FAO, 1995), and regulating atmospheric fluxes of greenhouse gases (Jenkinson, 199 1 ; Wallace, 1994).
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
2. 32 A.S. Moretto et al. / Applied Soil Ecology 18 (2001) 31–37
frequently associated with changes in species com- The most abundant species in the herbaceous layer
position in native grasslands (e.g. Westoby et al., are perennial C3 cool-season bunchgrasses (Distel and
1989; Milchunas and Lauenroth, 1993; Milton et al., Peláez, 1985). The palatable grasses (S. clarazii, P.
1994). In semi-arid grasslands of central Argentina, ligularis, S. tenuis, Piptochaetium napostaense) are
high-nutrient grasses frequently give way to invasion the dominant species, but individuals and patches of
by low-nutrient grasses under conditions of long-term unpalatable grasses (S. gynerioides, S. tenuissima, S.
heavy grazing (Llorens, 1995; Distel and Bóo, 1996). trichotoma, S. speciosa, S. brachichaeta) are common.
In this system, high-nutrient grasses are palatable to The leaves of the palatable grasses are higher in N con-
ungulate grazers, whereas low-nutrient grasses are un- centration and lower in C:N ratio and lignin concen-
palatable to ungulate grazers (i.e. they are consumed tration than those of the unpalatable grasses (Moretto
either to a greater or to a lower degree than expected and Distel, 1997). These differences in chemical com-
based on their abundance, respectively) (Distel et al., position translate into a high acceptability of palatable
2000; Pisani et al., 2000). Our study addresses the grasses and a low acceptability of unpalatable grasses
question of whether the palatable and unpalatable by ungulate grazers (Bóo et al., 1993).
grasses native to the temperate semi-arid grasslands
of central Argentina differ in decomposition rate and 2.2. Experimental design
nutrient release from leaf litter and roots.
The objective of this study was to compare de- In November 1995, plants of the two palatable
composition and N and P dynamics of Poa ligularis species (P. ligularis, S. clarazii) and of the unpalat-
and Stipa clarazii (palatable grasses) leaf litter and able species (S. tenuissima) were collected at their
roots, incubated at their source sites, with that of S. natural growing sites and taken to the laboratory. The
tenuissima (unpalatable grass) incubated at its source aboveground portion of each plant was sampled for
site. We hypothesized that leaf litter and roots from leaf material that had recently senesced and that was
the palatable grasses decompose and release nutrients still connected to the plant. The below-ground portion
faster than leaf litter and roots from the unpalatable was sampled for roots that were still attached to the
grasses. crown after removing the soil by gently washing with
tap water. It is probable that root samples contained
both living and recently dead roots. Leaf litter and
2. Materials and methods roots were air dried to constant weight at room tem-
perature, cut into 10 cm long pieces, and enclosed in
2.1. Study area 10 cm × 15 cm bags (5 g per bag) from polyethylene
gauze (0.35 mm mesh). A survey of soil fauna in the
The research was conducted in the Caldén Dis- region revealed that soil fauna larger than 0.35 mm is
trict (Cabrera, 1976), on an upland area located in the almost absent (Perez et al., 1987). For each studied
south-eastern zone of La Pampa province in central species, a subsample of the leaf litter and roots were
Argentina (38◦ 45 S; 63◦ 45 W). The 20 ha area has not weighed air-dry and again after 48 h in an oven at
been grazed by domestic animals for ∼20 years. The 60◦ C, in order to calculate initial oven-dry weights
climate is temperate, semi-arid. Mean monthly aver- of the material. On 15 March 1996, the leaf litter and
age day time air temperatures range from a low of root bags were transferred to native growing sites of
7◦ C in July to a high of 24◦ C in January, with an an- each of the species. Within sites with a continuous
nual mean of 15◦ C. Mean annual rainfall is 400 mm, cover either of P. ligularis, S. clarazii or S. tenuissima,
with peaks in October and March. The more severe 30 leaf litter bags were placed horizontally on the soil
droughts occur during summer. Precipitation during surface and 30 root bags were laid horizontally at the
the experimental period was 530 and 548 mm, in 1996 bottom of a hole (5 cm deep) and covered with the
and 1997, respectively. Dominant soils are coarse tex- removed soil. At each sampling date, 10 leaf litter or
tured Calciustolls. A petrocalcic horizon is commonly root bag of each species were retrieved. In this way,
found at depths of 60–80 cm. The physionomy of the 10 replicate leaf litter bags and 10 replicate root bags
vegetation is grassland with isolated woody plants. were collected for each species after 9, 16 and 21
3. A.S. Moretto et al. / Applied Soil Ecology 18 (2001) 31–37 33
months of incubation. In the laboratory, the leaf litter were performed to test differences among species
and roots were removed from the bags, cleaned to when F-values from ANOVAs were significant (P <
remove any extraneous organic material, and weighed 0.05). Pearson’s correlation coefficients were calcu-
after drying at 60◦ C for 48 h. Corrections for inor- lated for the percentage mass loss after 21 months
ganic contaminants (soil particles mainly) were made of incubation and initial leaf litter and root quality
after determining loss-on-ignition of all samples (4 h, parameters.
600◦ C).
Initial leaf litter and root samples were analyzed for
C, N, P, and lignin, whereas subsequent samples were 3. Results
analyzed for N and P. Carbon was determined by dry
combustion with an elemental analyzer (Leco). Nitro- Initial leaf litter and roots of the palatable grasses
gen was determined by semi-micro Kjeldahl, P ac- (S. clarazii and P. ligularis) were higher (P < 0.05)
cording the colorimetric technique of Olsen and Dean in N and P, and lower (P < 0.05) in lignin, C:N
(1965), and lignin using the detergent method (Goer- ratio, lignin:N ratio and lignin:P ratio than was the
ing and Van Soest, 1970). unpalatable grass (S. tenuissima). The only exception
Soil temperature and soil moisture were periodi- was the similarity in N content of roots between P.
cally measured during the experimental period at the ligularis and S. tenuissima (Table 1). Both groups of
native growing sites of each species. Soil temperature species differed more in leaf litter chemistry than in
(0–3 cm depth) was measured with copper–constantan root chemistry.
thermocouples (n = 6) at 14.00 h, whereas soil mois- The percentage mass remaining of leaf litter var-
ture (0–15 cm depth) was determined gravimetrically ied significantly (P < 0.01) with time and species
(n = 5). Precipitation during the study period was (Fig. 1). The interaction time by species was not sig-
measured with an automatic rain gauge located in the nificant (P > 0.05). The leaf litter of the palatable
study area. grasses decomposed faster (P < 0.05) than that of
Mass loss and N and P release data were expressed the unpalatable grass. After 21 months of incubation
as percentage of initial values on an ash-free basis. the percentage mass remaining of leaf litter was 58,
The expression of the N and P contents of the leaf lit- 59 and 78%, for S. clarazii, P. ligularis, and S. tenuis-
ter and root bags as a percentage of the initial content sima, respectively. On the other hand, the percentage
allowed for the determination of net N and P dynam- mass remaining of roots also varied significantly (P <
ics. All data were analyzed by a two-way (species 0.01) with time and species (Fig. 1), but there was a
and time) analysis of variance (ANOVA). Leaf litter time by species interaction (P < 0.05). On average,
and root data were analyzed separately. Mass loss of the roots of S. clarazii decomposed faster (P < 0.05)
roots was arcosine-square root transformed prior to than those of P. ligularis and S. tenuissima. After 21
analysis to improve normality. Tukey–Kramer tests months of incubation, the percentage mass remaining
Table 1
Initial chemical composition of ash-free leaf litter and rootsa
Lignin (%) N (%) P (%) C:N Lignin:N Lignin:P
Leaf litter
P. ligularis 3.9 a 1.6 a 0.06 a 26 a 2.4 a 63 a
S. clarazii 4.9 b 1.8 b 0.06 a 23 a 2.7 a 82 b
S. tenuissima 7.9 c 0.9 c 0.02 b 49 b 8.7 b 370 c
Roots
P. ligularis 13 a 1.1 a 0.06 a 35 a 11 a 227 a
S. clarazii 16 b 1.4 b 0.07 b 27 b 12 b 237 a
S. tenuissima 19 c 1.1 a 0.04 c 38 c 17 c 447 b
a Values are means of five samples. Values within a column and plant part followed by different letters are significantly different
(P < 0.05).
4. 34 A.S. Moretto et al. / Applied Soil Ecology 18 (2001) 31–37
Fig. 1. Ash-free mass remaining through time of leaf litter and roots from P. ligularis, S. clarazii and S. tenuissima. Values are means of
10 samples ± 1 S.E. At the end of the experiment values followed by different letters are significantly different (P < 0.05).
Fig. 2. Nitrogen and phosphorus content (as percentage of initial content) of ash-free leaf litter and roots from P. ligularis, S. clarazii and
S. tenuissima. Values are means of five samples ± 1 S.E. At the end of the experiment values followed by different letters are significantly
different (P < 0.05); n.s. indicates differences not significant (P > 0.05).
5. A.S. Moretto et al. / Applied Soil Ecology 18 (2001) 31–37 35
of roots was 51, 56 and 61%, for S. clarazii, P. ligu- soil organic matter in the system. It is necessary to no-
laris, and S. tenuissima, respectively. tice that although part of the roots used in this study
The P and N content of the leaf litter and root bags were probably live when collected, and might have not
(Fig. 2) varied significantly (P < 0.01) with time and adequately represented the chemical composition of
species, except for the differences among species in natural senesced roots, some evidence suggests min-
N content of the root bags. The interaction time by imal nutrient retranslocation from roots upon senes-
species was significant (P < 0.01), except for the cence (Oestertag and Hobbie, 1999; Wedin, 1999).
dynamic of N in the roots. In the first 9 months of The greater differences between palatable and un-
incubation there was net P and N release from the leaf palatable grasses in leaf litter than in root decomposi-
litter of the three species, except for P in S. tenuissima, tion and nutrient release were associated with a much
whereas in the last 12 months of incubation there was higher initial difference between them in leaf litter
a tendency to immobilize P and N in the leaf litter chemistry than in root chemistry (Table 1). All the
of all species. However, at the end of the incubation correlations between the percentage mass loss after
period there was net immobilization of P in the leaf 21 months of incubation and initial chemical param-
litter of the unpalatable species but net release of P eters were much stronger for leaf litter than for roots
from the leaf litter of the palatable species. In the case (Table 2). Since our decomposition experiment was
of N, although there was net release from the leaf performed at the native growing sites of each species, it
litter of all three species, it was lower (P < 0.05) in is not possible to separate the influence of litter chem-
the unpalatable than in the palatable species. On the istry from possible site differences in biotic and/or abi-
other hand, there were only minor differences among otic conditions. However, the similarities among sites
species in root P and N dynamics. There was a marked in soil temperature and soil moisture (Fig. 3) and their
release of P and N in the first 9 months of incubation, proximity, suggest that conditions for decomposition
and a slow tendency to release or immobilize P and were similar among them.
N after that. At the end of the incubation period the The P and N dynamics during the incubation period
percentage of P and N released from the roots of the (Fig. 2) indicate a relatively low potential to immobi-
unpalatable and palatable species was similar (P > lize nutrients in the leaf litter and roots of both palat-
0.05). able and unpalatable grasses. The exception was the
marked tendency to immobilize P in the leaf litter of S.
tenuissima, which was associated with the lowest ini-
4. Discussion tial P concentration (Table 1). When P concentration
is low, considerable immobilization of P from the soil
Our results only partly support the hypothesis that solution may be needed for decomposition to progress
decomposition and nutrient release are faster in P. (Gijsman et al., 1997). In contrast, late-seral grasses
ligularis and S. clarazii (palatable species) than in S.
tenuissima (unpalatable species). Although leaf litter
decomposition (Fig. 1) and nutrient release (Fig. 2) Table 2
Pearson correlation coefficients (r) (n = 15) between mass loss
were higher for the palatable grasses than for the un-
and initial litter quality parameters
palatable grass, there were no consistent differences
between them in root decomposition and nutrient re- Leaf litter Roots
lease. The exception were the roots of S. clarazii, Lignin −0.90∗∗∗ −0.22a
which on average decomposed faster than the roots of N 0.88∗∗∗ 0.55∗
P. ligularis and S. tenuissima. The overall similarities P 0.90∗∗∗ 0.71∗∗
C:N −0.89∗∗∗ −0.62∗∗
between the palatable and the unpalatable species in
Lignin:N −0.91∗∗∗ −0.45a
the decomposition and nutrient dynamics of roots is Lignin:P −0.91∗∗∗ −0.56∗
relevant because the ratio of below-ground to above- aP > 0.05.
ground biomass can be as high as 7:1 in the study site ∗ P < 0.05.
(Distel and Fernández, 1986), indicating that root pro- ∗∗ P < 0.01.
duction and turnover represent the major input of new ∗∗∗ P < 0.001.
6. 36 A.S. Moretto et al. / Applied Soil Ecology 18 (2001) 31–37
factors such as fire and drought (drought enhances
the amount of detritus for decomposition and nutrient
mineralization through increasing tissue mortality).
In our study system, because the unpalatable grasses
apparently have a low capacity to immobilize nutri-
ents, pulses of high nutrient availability caused by fire
and/or drought (historically recurrent in the system;
Distel and Bóo, 1996) may have created opportuni-
ties for plant species with high resource requirements
(palatable species) to maintain dominance within
natural communities. Plants with high nutrient re-
quirements commonly have higher rates of nutrient
uptake and growth and, consequently, higher compet-
itive ability (Grime, 1979). Previous results showed
that the competitive ability of the palatable grasses
is higher than that of the unpalatable grasses in the
studied system (Moretto and Distel, 1997). Grazing
is other factor that can also increase soil nutrient
availability (McNaughton et al., 1988; McNaughton
et al., 1997), and may, therefore, favor dominance
of the palatable species. However, the high nutrient
availability states induced by grazing may be un-
Fig. 3. Superficial soil (0–3 cm depth) temperature and percentage stable under heavy and continuous selective grazing
of soil (0–15 cm depth) moisture in P. ligularis, S. clarazii and S.
by domestic animals, leading to reduced dominance
tenuissima. Values are means of five samples.
of palatable species in favor of unpalatable species
(Jefferies et al., 1994; Pastor and Cohen, 1997). Ex-
from relatively humid environments have a high ca- perimental evidence (Anderson and Briske, 1995;
pacity to immobilize nutrients (Wedin, 1995). Wedin Moretto and Distel, 1999) supports the hypothesis
(1999) presented a conceptual model of the depen- that selective defoliation of the palatable species con-
dence of N availability on litter quality. It assumes that fers a competitive advantage to unpalatable species,
a C:N ratio of roughly 30 for plant litter represents the which could ultimately lead to species replacement in
breakpoint above which there is net immobilization of grasslands.
N and below which there is net mineralization of N.
In our study, the C:N ratio of the litter of all species Acknowledgements
was close to this threshold, except for the C:N ratio
of the leaf litter of the unpalatable grass (C:N ratio of This research was supported by the Universidad
48, Table 1). As predicted by the model, the greatest Nacional del Sur, the Consejo Nacional de Inves-
immobilization of N occurred in the leaf litter of the tigaciones Cient´ficas y técnicas (CONICET) de la
ı
unpalatable species. República Argentina, and the Agencia Nacional de
The capacity to immobilize nutrients of the species Promoción Cient´fica y Tecnológica (ANPCyT) de la
ı
present in an ecosystem may have important implica- República Argentina. A fellowship from CONICET
tions with regards to plant community dynamics and to A.S. Moretto is also acknowledged.
stability (Wedin, 1999). The lower the capacity to
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