Dataset Information

Leaf P increase outpaces leaf N in an Inner Mongolia grassland over 27 years.

ABSTRACT: The dynamics of leaf nitrogen (N) and phosphorus (P) have been intensively explored in short-term experiments, but rarely at longer timescales. Here, we investigated leaf N : P stoichiometry over a 27-year interval in an Inner Mongolia grassland by comparing leaf N : P concentration of 2006 with that of 1979. Across 80 species, both leaf N and P increased, but the increase in leaf N lagged behind that of leaf P, leading to a significant decrease in the N : P ratio. These changes in leaf N : P stoichiometry varied among functional groups. For leaf N, grasses increased, woody species tended to increase, whereas forbs showed no change. Unlike leaf N, leaf P of grasses and forbs increased, whereas woody species showed no change. Such changes may reflect N deposition and P release induced by soil acidification over the past decades. The interannual effect of precipitation may somewhat have reduced the soil available N, leading to the more modest increase of leaf N than of leaf P. Thus, leaf N : P stoichiometry significantly responded to long-term environmental changes in this temperate steppe, but different functional groups responded differently. Our results indicate that conclusions of plant stoichiometry under short-term N fertilization should be treated with caution when extrapolating to longer timescales.

SUBMITTER: Mi Z

PROVIDER: S-EPMC4321160 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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Leaf P increase outpaces leaf N in an Inner Mongolia grassland over 27 years.

Mi Zhaorong Z Huang Yuanyuan Y Gan Huijie H Zhou Wenjia W Flynn Dan F B DF He Jin-Sheng JS

Biology letters 20150101 1

The dynamics of leaf nitrogen (N) and phosphorus (P) have been intensively explored in short-term experiments, but rarely at longer timescales. Here, we investigated leaf N : P stoichiometry over a 27-year interval in an Inner Mongolia grassland by comparing leaf N : P concentration of 2006 with that of 1979. Across 80 species, both leaf N and P increased, but the increase in leaf N lagged behind that of leaf P, leading to a significant decrease in the N : P ratio. These changes in leaf N : P st ...[more]

PMID: 25589490

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Project description:Enclosure and grazing can significantly change the turnover of nitrogen in grassland soil. Changes of soil nitrogen mineralization and ammonium-oxidizing microorganisms caused by enclosure in different grazing intensities (about 30 years of grazing history) grassland, however, has rarely been reported. We selected the grassland sites with high and medium grazing intensity (HG and MG, 4 and 2 sheep ha-1, respectively) and had them enclosed (45 × 55 m) in 2005 while outside the enclosure was continuously grazed year-round. A two factorial study was designed: grazing intensity (MG and HG sites) and enclosure (fence and non-fence). Nitrogen mineralization was detected through a laboratory incubation experiment. The abundance and community structure of soil ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were analyzed using quantitative PCR (q-PCR), terminal-restriction fragment length polymorphism (T-RFLP), cloning, and sequencing. Results showed that compared with MG site, at HG site the AOB abundance and community structure of AOB changed significantly while the AOA abundance and community structure did not change obviously. Enclosure significantly decreased the cumulative mineralized N, N mineralization rate, the abundance of AOB and the AOB community structure at the HG site, while at MG site, enclosure did not change these parameters. Potential nitrification rate (PNR) was positively correlated with the abundance of AOA and AOB at the MG and HG sites, respectively. The abundance of AOA was significantly correlated with soil pH; however, AOB abundance was significantly correlated with soil available N, total N, C/N ratio, pH, etc. The phylogenetic analysis showed that Nitrososphaeraceae and Nitrosomonadaceae were the dominant AOA and AOB, respectively. Totally, the responses of AOB and AOA mainly were associated to changes in soil physicochemical properties caused by different intensity grazing; AOB and AOA may be the dominant functional players in ammonia oxidation processes at HG and MG site, respectively.

Project description:BackgroundNumerous studies have shown that nitrogen (N) deposition decreases biodiversity in terrestrial ecosystems. To explain the N-induced species loss, three functionally based hypotheses have been proposed: the aboveground competition hypothesis, the belowground competition hypothesis, and the total competition hypothesis. However, none of them is supported sufficiently by field experiments. A main challenge to testing these hypotheses is to ascertain the role of shoot and root competition in controlling plant responses to N enrichment. Simultaneously examining both aboveground and belowground responses in natural ecosystems is logistically complex, and has rarely been done.Methodology/principal findingsIn a two-year N addition experiment conducted in a natural grassland ecosystem, we investigated both above- and belowground responses of plants at the individual, species, and community levels. Plants differed significantly in their responses to N addition across the different organizational levels. The community-level species loss was mainly due to the loss of perennial grasses and forbs, while the relative abundance of plant species was dependent mainly on individual-level responses. Plasticity in biomass allocation was much smaller within a species than between species, providing a biological basis for explaining the functionally based species loss. All species increased biomass allocation to aboveground parts, but species with high belowground allocations were replaced by those with high aboveground allocations, indicating that the increased aboveground competition was the key process responsible for the observed diversity loss after N addition in this grassland ecosystem.Conclusions/significanceOur findings shed new light on the validity of the three competing hypotheses concerning species loss in response to N enrichment. They also have important implications for predicting the future impacts of N deposition on the structure and functioning of terrestrial ecosystems. In addition, we have developed a new technique for ascertaining the roles of aboveground and belowground competition in determining plant responses to N fertilization.

Project description:Background and aimsOrchids are known to be particularly sensitive to environmental changes due to their narrow ranges of secondary successional habitats. Lack of data at the community level limits our ability to evaluate how traits of different species influence their responses to habitat change. Here, we used a diachronic survey of Mediterranean orchid communities in Corsica to examine this question.MethodsUsing data from two field surveys conducted 27 years apart (1982-84 and 2009-11) at the same 45 sites in Corsica, we evaluated the impact of increase in woody plant cover (WPC) on (i) the richness and composition and (ii) the local extinction/colonization dynamics of orchids. We applied a Bayesian multispecies site-occupancy model to each of the 36 orchid species recorded at these sites to estimate the detection probability of each species, enabling us to account for under-detection in estimating their dynamics.Key resultsBetween 1982 and 2011, WPC changed at 82·3 % of sites (increasing at 75·6 %, decreasing at 6·7 %). Despite marked changes in composition of orchid communities at the local scale, no significant change was detected in species richness at the regional scale. Canopy closure affected the probability of new colonization of sites, but had no significant influence on the probability of local extinction. However, the abundance of shade-intolerant species declined more sharply than that of shade-requiring species. Among orchid species, the detection probability was significantly and positively correlated with population density and plant height.ConclusionsThis study reveals contrasted dynamics of orchid communities between local and regional scales in Corsica. Although high turnover in communities was found at the local scale, regional species richness was maintained despite major land-use changes. Conserving landscape mosaics could provide locally suitable habitats for orchids of different ecologies to maintain diversity at larger spatial scales.

Dataset Information

Leaf P increase outpaces leaf N in an Inner Mongolia grassland over 27 years.

Publications

Leaf P increase outpaces leaf N in an Inner Mongolia grassland over 27 years.

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