Plant carbon (C) and nitrogen (N) stoichiometry play an important role in the maintenance of ecosystem structure and function. To decipher the influence of changing environment on plant C and N ...stoichiometry at the subcontinental scale, we studied the shoot and root C and N stoichiometry in two widely distributed and dominant genera along a 2,200‐km climatic gradient in China's grasslands. Relationships between C and N concentrations and soil climatic variables factors were studied. In contrast to previous theory, plant C concentration and C:N ratios in both shoots and roots increased with increasing soil fertility and decreased with increasing aridity. Relative N allocation shifted from soils to plants and from roots to shoots with increasing aridity. Changes in the C:N ratio were associated with changes in N concentration. Dynamics of plant C concentration and C:N ratios were mainly caused by biomass reallocation and a nutrient dilution effect in the plant‐soil system. Our results suggest that the shifted allocation of C and N to different ecosystem compartments under a changing environment may change the overall use of these elements by the plant‐soil system.
We investigated spatial variations of plant above‐and belowground C and N stoichiometry for two dominant genera along a unique large‐scale (2200‐km) transect in China's grasslands. Contrast to previous theory, plant C concentration and C:N ratios in both shoots and roots increased with precipitation and soil fertility but decreased with temperature. Relative N allocation increased from soil to plants and within plants from roots to shoots with increasing aridity.
Anthropogenic nitrogen (N) deposition has affected plant community composition and nutrient cycling in terrestrial ecosystems worldwide. This includes changes to the way plants use and recycle ...nutrients, including effects on nutrient resorption, which is a key process through which plants recover nutrients from tissue during senescence. Nutrient resorption has considerable adaptive and functional significance for plants and helps regulate core ecosystem processes such as decomposition. However, our understanding of how N deposition affects nutrient resorption and, in particular, of how N inputs alter ecosystem resorption via changes to existing species’ resorption compared with changes to community composition remains poor. To disentangle the role of species
versus
community composition controls driving variation in nutrient resorption responses to N inputs, we carried out an experiment with six different N addition rates in a temperate steppe. We found that species-scale nutrient resorption responses to N enrichment were variable; for example, only half of the measured species reduced both N and P resorption efficiency in response to increased N inputs. In contrast, community-scale responses consistently resulted in reduced N and P resorption. Still, N-induced changes in community composition were a weaker control on overall resorption responses than were the effects on individual species; however, it was the synergistic interaction between the two that resulted in the large total reductions of nutrient resorption in the face of increased N. Taken together, our results highlight that understanding and predicting nutrient resorption responses will be most accurately scaled by accounting not only for species’ reductions in resorption but also for changes in community composition.
BACKGROUND AND AIMS: Stoichiometric relations drive powerful constraints on many ecosystem processes. However, our understanding of the hierarchical responses of plant C:N:P stoichiometry at ...different levels of biological organization to global change factors remains limited. METHODS: we examined the plant C:N:P stoichiometric responses to N deposition and mowing (hay making) at both species- and community-level by carrying out a 4-year field experiment in the temperate steppe of northern China. RESULTS: Our results showed that N addition and mowing resulted in higher plant N concentrations, lower C:N, and higher N:P at both species- and community-level. Mowing had a limited negative influence on the effects of N addition. We observed divergent responses of both plant P concentrations and C:P to N addition at species-level and community-level: N addition led to higher plant P and lower C:P at species-level, but this effect was not observed at the community-level. CONCLUSIONS: Our results indicate that stoichiometric responses at community-level to N addition and mowing diverge from more traditionally examined species-specific responses. Our results suggest that the hierarchical responses of plant stoichiometry to anthropogenic disturbance deserves more attention when we model the interactions of terrestrial ecosystem C, N, and P cycling under scenarios of increasing N availability concomitantly occurring with active land management.
The effects of global change factors on the stoichiometric composition of green and senesced plant tissues are critical determinants of ecosystem feedbacks to anthropogenic-driven global change. So ...far, little is known about species stoichiometric responses to these changes. We conducted a manipulative field experiment with nitrogen (N; 17.5 g m⁻² year⁻¹ ) and water addition (180 mm per growing season) in a temperate steppe of northern China that is potentially highly vulnerable to global change. A unique and important outcome of our study is that water availability modulated plant nutritional and stoichiometric responses to increased N availability. N addition significantly reduced C: N ratios and increased N: P ratios but only under ambient water conditions. Under increased water supply, N addition had no effect on C: N ratios in green and senesced leaves and N: P ratios in senesced leaves, and significantly decreased C: P ratios in both green and senesced leaves and N: P ratios in green leaves. Stoichiometric ratios varied greatly among species. Our results suggest that N and water addition and species identity can affect stoichiometric ratios of both green and senesced tissues through direct and interactive means. Our findings highlight the importance of water availability in modulating stoichiometric responses of plants to potentially increased N availability in semi-arid grasslands.
Atmospheric nitrogen (N) deposition is altering grassland productivity and community structure worldwide. Deposited N comes in different forms, which can have different consequences for productivity ...due to differences in their fertilization and acidification effects. We hypothesize that these effects may be mediated by changes in plant functional traits. We investigated the responses of aboveground primary productivity and community functional composition to addition of three nitrogen compounds (NH
4
NO
3
, NH
4
2
SO
4
, and CONH
2
2
) at the rates of 0, 5, 10, 20 g N m
−2
yr
−1
. We used structural equation modeling (SEM) to evaluate how functional structure influences the responses of productivity to the three N compounds. Nitrogen addition increased community-level leaf chlorophyll content but decreased leaf dry matter content and phosphorus concentration. These changes were mainly due to intra-specific variation. Functional dispersion of traits was reduced by N addition through changes in species composition. SEM revealed that fertilization effects were more important than soil acidification for the responses of productivity to CO(NH
2
)
2
addition, which enhanced productivity by decreasing functional trait dispersion. In contrast, the effects of (NH
4
)
2
SO
4
and NH
4
NO
3
were primarily due to soil acidification, influencing productivity via community-weighted means of functional traits. Our results suggest that N forms with different fertilizing and acidifying effects influence productivity via different functional traits pathways. Our study also emphasizes the need for in situ experiments with the relevant N compounds to accurately understand and predict the ecological effects of atmospheric N deposition on ecosystems.
Aims
The stoichiometric traits of litter play an important role in driving litter decomposition and ecosystem nutrient cycling. While the impacts of nitrogen (N) deposition on the species-level ...litter stoichiometric traits have been well addressed, we know little about that at community-level, which is supposed to be driven by both intra-specific variation and changes in community composition.
Methods
We examined the effects of N deposition on litter phosphorus (P) concentration and N:P ratio at both species- and community-level in a semi-arid grassland of northern China. We further decomposed the community-level variations of litter nutritional traits into intra- and inter-specific variation.
Results
Nitrogen addition, especially at high rates, substantially changed community composition. Litter P concentrations and N:P ratios significantly varied among different species. Litter P concentrations and N:P ratios at both species- and community-level were positively correlated with N addition rates. Biomass-weighted community-level N:P ratios were more sensitive to N addition than the non-weighted ones, indicating that community composition strengthened the positive impacts of N addition on litter N:P ratios. There was positive co-variation between intra- and inter-specific variation for litter N:P ratio, indicating the consistency of community composition and intra-specific variation in their effects on litter N:P ratio.
Conclusions
Our results indicated that the imbalance of N and P following N enrichment would be much larger than the expectation based on the findings from species-level, and thus highlight the importance of changes in community composition in driving the responses of community-level litter N:P stoichiometry to N deposition in the semi-arid grassland.
Aims The responses of functional structures in plant communities to global change drivers is predicted to be driven by both species turnover and intraspecific trait variability (ITV). However, the ...relative importance of those two drivers is not well-known, which retards our ability to predict the functional changes of plant community under global change scenarios. We hypothesized that ITV rather than species turnover would drive the nutritional responses of plant community at the initial stage after nitrogen and water enrichment. Methods We measured community weighted means (CWM) and non-weighted means (CM) of foliar N and P concentrations and N:P ratio in a temperate steppe after two years factorial N and water addition. Species composition and nutrition traits of each species were recorded in each plot. Results The impacts of N addition on community level nutrition traits were highly dependent on water conditions, as indicated by significant interactive effects between N and water addition. Nitrogen addition significantly increased CWM of foliar N, but only under ambient water condition. Water addition decreased CWM of foliar P and increased that of N:P. Consistent with our hypothesis, communities responded to both N and water addition after two years treatments mainly through ITV. Conclusions Our results highlight the importance of ITV in driving short-term responses of community functional composition to the increases of nitrogen and water availability in the temperate steppe. The existence of interactive effects of N and water addition would make it more difficult to predict the impacts of N deposition on plant-mediated biogeochemical cycling under the scenarios of precipitation regime changes than previously assumed.
Aims
Uncovering the importance of soil and plant characteristics in driving the legacy effects of nitrogen (N) deposition on plant community nutrient stoichiometry would improve our understanding of ...plant-soil interaction during restoration of historically N-enriched ecosystems.
Methods
Based on a field experiment with the cessation of six-year N addition in a temperate steppe of northern China, we measured concentrations and stoichiometry of N and phosphorus (P) in soils and different plant functional groups, under both mown and unmown conditions.
Results
Historical N addition did not affect soil total and available N and P concentrations and stoichiometry, but significantly altered plant community composition. Plant nutrient concentrations and N:P ratios significantly differed among four plant functional groups. The concentrations and stoichiometric ratios of N and P between soils and plants were generally not correlated. The positive legacy effects of N addition on community N:P stoichiometry were caused by the biomass enhancement of tall bunchgrass, the functional group with the highest N:P ratios.
Conclusions
Changes in plant community composition instead of soil nutrient status were the main driver for the positive legacy effects of N enrichment on plant community stoichiometry. Given that the recovery of community composition after the cessation of N deposition is generally slow, our findings indicate that the legacy effects of N deposition on soil nutrient cycling would persist in long-term due to the importance of plant-mediated pathway.
Combining nutrient dynamics (plant nutrient uptake and soil fertility) can help uncover mechanisms of shrub–grass interactions and assess the validity of the stress‐gradient hypothesis, which ...predicts that facilitation between plants increases in stressful environments. However, how facilitation via shrub‐mediated nutrient increases varies with precipitation is poorly resolved.
We first synthesized a global dataset from 66 studies and evaluated how shrubs affected soil organic carbon (C) and nitrogen (N) in grasslands along a precipitation gradient. We then made new measurements in a single‐grassland type encroached by leguminous shrubs from the same genus (Caragana) to constrain the variations caused by combining different grassland types and shrubs traits in the meta‐analysis. Specifically, we investigated how shrubs mediated N dynamics and how shrub–grass interactions varied along a precipitation gradient (147–342 mm) in a temperate steppe of China.
At the global scale, leguminous shrub‐mediated effects on soil nutrients increased with precipitation, while no relationship was found for non‐leguminous shrub. For the field experiment, greater N and lower δ15N in Caragana compared to non‐leguminous shrub (reference shrub, Salsola collina) suggested active N‐fixation in Caragana. We found that Caragana enhanced N concentration and leaf quality (low C:N ratio) in neighbouring plants more on mesic sites than on xeric sites. Thus, facilitation increased via higher soil N and with decreasing environmental stress, at least along this relatively arid precipitation gradient.
Our results highlight the importance of precipitation in determining the nutritional facilitation to neighbouring grasses from encroaching leguminous shrubs. Conceptual frameworks for plant facilitation may therefore need to include shrub characteristics (N‐fixers vs. non‐fixers) and positive effects of higher precipitation on this type of facilitation to characterize plant interactions along stress gradients.
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