Oecologia最新文献

Aggregations of plants surrounded by sparsely vegetated areas in drylands can arise when larger plants facilitate the recruitment of smaller "protégé" plants-a phenomenon referred to as the "nurse plant" effect. Numerous drivers can generate a nurse plant effect; efforts to simultaneously quantify multiple drivers are rare. Given higher densities of protégés beneath the foundational shrubs Larrea tridentata and Neltuma glandulosa, multiple potential mechanisms underlying the nurse plant effect were quantified in the Chihuahuan Desert, New Mexico, USA. As expected, there was a greater concentration of soil nutrients and lower photosynthetically active radiation and soil temperatures beneath shrubs. Throughout the study, however, soil moisture was consistently higher in interspaces despite the greater water holding capacity of soils beneath shrubs. Nutrient concentrations were greater beneath N. glandulosa than L. tridentata, while protégé numbers did not significantly differ among the species. The canopy size of both species was positively related to understory shading, and the size of N. glandulosa was positively related to soil nitrogen and microbial biomass. The results of this study suggest that much of the abiotic nurse plant effect of this low-latitude system is explained by radiation interception and concomitant reductions in temperatures experienced by protégé plants as opposed to the direct effects of shrubs on soil water availability. As global change pressures intensify in drylands, a loss of perennial plant cover could have negative effects on soil biogeochemical pools and plant diversity. Quantification of the mechanisms driving the nurse plant effect across environmental and climatic gradients could improve our understanding of plant community dynamics in drylands.

The functional traits of angiosperm vessels influence water transport and, therefore, metabolism and performance. Among these traits is a trade-off between vessel diameter and number, known as the "packing rule", which has been abundantly confirmed. But how packing rule is connected to major dimensions of variation in hydraulic function remains unclear across and within diverse species. Using data from the primary literature spanning 3992 species for intraspecific data and 54 species for interspecific data, and newly acquired data from the branches of 80 tree species, we examine the ways that key xylem traits plus leaf mass covary with the packing rule for stems across and within species. We analyzed vessel diameter, individual vessel lumen area, vessel density (number of vessels per unit area), lumen fraction (the product of individual vessel lumen area and vessel density), non-vessel lumen fraction (total area minus total lumen area), specific stem conductivity, and wood density. Mean vessel lumen area scaled approximately as the - 1.0 power of vessel density across the pooled data. Little variation in the lumen fraction was attributable to total vessel lumen area, whereas the lumen fraction was positively correlated with vessel density in stems and branches across all species. Wood density was weakly negatively correlated with mean vessel lumen area, but was not correlated with either lumen or non-vessel lumen fractions in branches or stems across species. Vessel area scaled positive with leaf mass. Specific stem conductivity was correlated with mean vessel lumen area and wood density. These results validate and extend the implications of the packing rule, and identify and define the limits of hydraulic efficiency and safety strategies within and across angiosperm species.

Herbivores significantly influence plant communities by modifying interspecies relationships, which in turn impacts ecosystem functioning. Although excluding herbivores is expected to enhance the dominance of perennial plants, few studies have consistently explored how plants adjust the growth-defense-reproduction trade-off in response to changes at different stages of herbivore exclusion. We conducted a controlled fence experiment in Inner Mongolia grassland to examine the effects of vole exclusion on the dominance and adaptation strategies of two perennial grasses. We found that twelve years of Brandt's vole grazing altered the plant community composition, but in the second year of the exclusion experiment, Leymus chinensis quickly regained its dominance. This rapid recovery was facilitated by L. chinensis strategically shifting its growth-defense-reproduction investment over time. In the early exclusion phase, L. chinensis quickly enhanced its competitive edge by prioritizing vegetative growth and clonal reproduction. As the exclusion period progressed, the species transitioned to seed-based dispersal to enhance population fitness. In contrast, the dominance of Cleistogenes squarrosa was largely influenced by interspecific interactions rather than intrinsic adaptive changes. These results reveal plants can dynamically adjust their resource investment strategies to optimize population fitness at different stages of vegetation recovery. This enhances our understanding of plant community dynamics and the establishment and maintenance of dominant species in grassland ecosystems.

Energy acquisition and risk avoidance can drive prey activity, but mechanistic understanding of the process through which prey traits mediate this energy-safety trade-off is lacking. We analyzed daily activity in winter of two winter-adapted prey that differ in antipredator strategies and physiological constraints on activity: snowshoe hares (Lepus americanus) and North American porcupines (Erethizon dorsatum). First, we constructed an energetics-based model to predict daily activity time for each species based on temperature and corresponding mass-dependent thermoregulatory costs. We then examined what factors drove the deviations of observed activity from the model prediction based on energy balance, considering individual variation. Neither hares nor porcupines achieved energy balance when temperatures fell below the thermoneutral zone. Activity deviations of hares from energy balance were explained by environmental factors associated with risk and energetics, with nominal individual variation being exhibited. In contrast, activity deviations of porcupines were independent of the environmental factors, and porcupines exhibited pronounced individual variation in activity. Our findings highlight that antipredator strategies and physiological constraints on activity can mediate the behavioral energy-safety trade-off of prey. Notably, morphological protection and energy reserves facilitate behavioral flexibility by relaxing the energy-safety trade-off, whereas dependence on behavioral predator avoidance limits the behavioral flexibility of prey.

Body size shifts of insular organisms have been widely observed, but few studies have simultaneously tested the combined and cascading effects of biotic and abiotic factors on morphological shifts. Here, we used two body size metrics (body length and body mass) of a small rodent (Rattus losea) to investigate its morphological shifts and the cascading mechanisms in the Zhoushan Archipelago, China. We used the live-trapping method to capture rodents and compared body size metrics between insular and mainland populations. We then constructed linear regression models to examine the relationships between the body size of rodents and three island attributes (island area, island isolation, and land use). Finally, we used structural equation modeling (SEM) to determine the cascading influences of three island attributes and four biotic factors (predator species richness, net primary productivity (NPP), capture rate, and rodent species richness) on body size. Island rodent populations had significantly larger body length and body mass than mainland counterparts. Both body length and body mass of insular rodents were negatively correlated with island area. SEMs showed that predator species richness had positive impacts on body length and body mass of insular rodents, while NPP had a negative effect on body mass. Moreover, SEMs revealed that island area positively influenced predator species richness, whereas land use negatively affected NPP. Body size shifts of the small rodent follow the prediction of the island rule (insular gigantism of small-sized species), but the determinants were strongly affected by which body size metrics were used. Therefore, both body length and body mass should be included in future studies to obtain a comprehensive understanding of the mechanisms underlying the body size shifts.

Trait plasticity is critical to maintaining grassland productivity under climate change, such as drought. However, few studies have focused on the effects of multiyear extreme drought on community-level fine root traits and their corresponding links to productivity. We experimentally removed 66% of growing season precipitation for four years in meadow, typical, and desert grasslands in northern China and evaluated the effects of multiyear drought on community-weighted means (CWMs) and functional diversity of fine root traits (first-order roots), and their relationships with aboveground net primary productivity (ANPP). We found that, in general, root functional composition (CWMs and functional diversity) showed no significant responses to prolonged, extreme drought across all sites. Additionally, ANPP was positively correlated with CWMs of fine root carbon: nitrogen ratio within and across both control and drought plots, indicating that a high abundance of dominant species with high nitrogen-use efficiency promotes ANPP under droughts. In contrast, we found no significant relationship between functional diversity of fine root traits and ANPP. Our results demonstrate that fine root traits at the community level in semiarid grasslands remain relatively stable in response to long-term extreme drought. These findings provide important insights into the responses of fine root traits to extreme drought and highlight their critical roles in predicting the responses of ecosystem functions in these grasslands.

Litter decomposition is one of the largest carbon (C) fluxes in terrestrial ecosystems and links aboveground biomass to soil C pools. In grasslands, decomposition drivers have received substantial attention but the role of grassland herbivores in influencing decay rates is often ignored despite their potentially large effects on standing biomass and nutrient cycling. Recent work has demonstrated that nutrient addition increases early-stage decay and suppresses late-stage decay. Mammalian herbivores can mediate the effects of nutrient supply on biomass, suggesting herbivores may alter the effects of nutrients on decomposition, though this is largely unknown. We examined how herbivory mediates the effects of nutrient supply on long-term decomposition across 19 grassland sites of the Nutrient Network distributed experiment. At each site, a full-factorial experiment of combined nitrogen (N), phosphorus (P), and micronutrient (K) enrichment ('control' or ' + NPK') and mammalian herbivore (> ~ 50 g) exclusion ('unfenced' or 'fenced') was carried out in a randomized block design. We hypothesized that nutrient effects on litter decomposition would be strongest where herbivores caused the greatest reductions in aboveground plant biomass (i.e., at sites with more intense herbivory). After accounting for wide variation in decomposition rates across sites, we found that, within sites, elevated nutrients increased early-stage decay and suppressed late-stage decay. In contrast, neither herbivore exclusion (i.e., fencing) nor site level changes in aboveground biomass due to herbivory altered the nutrient effects on decomposition rates. Across grasslands, our results indicate that elevated nutrient supply modifies litter decomposition rates independent of herbivore impacts.

Plants are likely to experience multiple cycles of drought. However, physiological acclimation and stress memory may play key roles in reducing the detrimental effects of successive droughts. We investigated drought acclimation in cotton (Gossypium hirsutum) fertilized with low or high nitrogen (N) in a greenhouse factorial experiment. The cotton plants were subjected to one of four drought treatments applied during two 15-day periods, where plants were withheld water or were fully watered. We assessed CO₂ assimilation (A₄₀₀) and stomatal conductance (g_s400), maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO) carboxylation (V_cmax), maximum rates of electron transport for RuBP regeneration (J_max), and biomass at the time of harvest. Droughted and well-watered plants had similar rates of A₄₀₀, g_s400, V_cmax, and J_max during the first drought under low N. High N plants were larger in size than low N plants, which suggests that the additional N likely increased the severity of the drought, causing stomatal closure and a decline in photosynthesis. However, there were increases in both V_cmax and J_max for high N plants during the first drought. There was no evidence of drought memory, and plants exposed to both droughts responded similarly to plants exposed to only the second drought. Overall, our results indicate that cotton can acclimate under drought, and additional fertilization may result in severe drought stress.

Stomatal closure is a pervasive response among trees exposed to flooded soil. We tested whether this response is caused by reduced hydraulic conductance in the soil-to-leaf hydraulic continuum (k_total), and particularly by reduced root hydraulic conductance (k_root), which has been widely hypothesized. We tracked stomatal conductance at the leaf level (g_s) and canopy scale (G_s) along with physiological conditions in two temperate tree species, Magnolia grandiflora and Quercus virginiana, that were subjected to flood and control conditions in a greenhouse experiment. Flooding reduced g_s, G_s, k_root and k_total. Path analysis showed strong support for direct effects of k_total on g_s and for flood duration on k_total, but not k_root on k_total. A process-based model that accounted for the k_total reduction predicted the timeseries of G_s in flood and control treatment trees reasonably well (predicted versus observed G_s R² = 0.80 and 0.51 for M. grandiflora and Q. virginiana, respectively). However, accounting only for k_root reduction in flooded trees was insufficient for predicting observed G_s reduction. Together, these results suggest that hydraulic constraints were not limited to roots and highlight the need to account for flooding effects on k_total when projecting forest ecosystem function using process-based models.

Understanding changes to local communities brought about by biological invasions is important for conserving biodiversity and maintaining environmental stability. Scale insects (Hemiptera: Coccoidea) are a diverse group of insects well known for their invasion potential and ability to modify local abundance of multiple insect groups. Here, we tested how the presence of crape myrtle bark scale (Acanthococcus lagerstroemiae, CMBS), an invasive felt scale species, seasonally impacted local insect abundance, biodiversity, and community structure on crape myrtle trees. Our field surveys showed that CMBS-infested trees had seasonal changes to local insect abundance and family-level richness, and inverse Simpson's diversity relative to non-infested trees. CMBS infestation resulted in a decrease in community evenness on crape myrtle trees. Community compositions of insect visitors were distinct between infested and non-infested trees. CMBS-infested trees had greater seasonal abundances of Coccinellidae, Vespidae, Dolichopodidae, and Muscidae. Two of the families (Coccinellidae, Vespidae) that responded most strongly to CMBS infestation were dominated by non-native species. Our results show that CMBS-infested trees acted as resource hubs for natural enemies and carbohydrate scavengers, resulting in uneven communities shaped by a few highly responsive taxa. The temporal dynamics of these effects support CMBS as an ecological catalyst, reshaping urban insect communities and highlight its potential for facilitating invasion cascades in anthropogenic habitats. These results emphasize the importance of fine-scale temporal monitoring for understanding and mitigating the ecological impacts of introduced scale insects in urban environments.