Facilitation by leguminous shrubs increases along a precipitation gradient

Abstract

Abstract1. Combining nutrient dynamics (plant nutrient uptake and soil fertility) can help uncover mechanisms of shrub-grass interactions and assess the validity of the stressgradient 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.2. 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.3. 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 δ 15 N 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. 4. 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.

Functional identity enhances aboveground productivity of a coastal saline meadow mediated by Tamarix chinensis in Laizhou Bay, China

“…These factors were notably and positively related to T. chinensis coverage based on the Pearson correlation test (r = 0.4-0.7, see Appendix 1), indicating soil fertility increased with T. chinensis coverage, and confirming the existence of the facilitation effect. Previous studies also demonstrated that net facilitation effect was more likely to occur in stressful environments 39 . Specifically, the formation of fertile islands is an important process driving the positive interactions between shrubs and grass 39 .…”

“…Previous studies also demonstrated that net facilitation effect was more likely to occur in stressful environments 39 . Specifically, the formation of fertile islands is an important process driving the positive interactions between shrubs and grass 39 .…”

Effects of forest preservation, livestock exclusion, and use of shrubs as potential nurses on planting success of an endangered tree

“…In this context, the preserved forest can provide protection from solar radiation and frost, as well as increased water content and litter accumulation, with the consequent increase in nutrients (Abiyu et al 2017). In particular, leguminous plants often provide litter with a high content of nutrients, mainly nitrogen, and facilitate the establishment and growth of other species (Avendaño‐Yáñez et al 2018; Zhang et al 2018 b ). Our results partially support these findings, because the preserved forest had higher nitrate and organic matter values than the degraded forest, whereas in the latter, nitrate and organic matter slightly increased from plots with herbaceous vegetation to microsites under shrubs, with the highest values being recorded under the leguminous spiny shrub.…”

Interacting water, nutrients, and shrub age control steppe grass‐on‐shrub competition: Implications for restoration

“…It can be expected, however, that the differential use of different essential resources by neighbor plants influences the outcome of their interaction (Tilman, 1982). Surprisingly, the experimental assessment of both the independent and joint effects of the availability of several essential soil resources on grass–shrub interactions, and on plant interactions in general, is scarce, yet findings so far suggest that the response of the plant interactions may not be consistent for the various resources considered (e.g., le Bagousse‐Pinguet et al, 2013; Wilberts et al, 2014; Zhang, Lü, et al, 2018), even for different sources of nitrogen (Trinder et al, 2012).…”

“…Furthermore, the relative importance of the mechanisms involved in herbaceous–woody plant interactions often changes as plants age, resulting in ontogeny‐mediated shifts in the outcome of the interactions, which in turn may vary in response to variations in abiotic conditions (le Roux et al, 2013; Soliveres et al, 2010). Overall, a growing body of literature points to the interplay between multiple factors regulating grass–shrub coexistence and interactions, yet there are still very few insights about the relative role and combined effects of the factors involved (Cipriotti et al, 2014; le Roux et al, 2013; Soliveres et al, 2015; Zhang, Lü, et al, 2018). The understanding of such interplay remains very limited, hampering our ability to predict the response of herbaceous–woody assemblages to changing climatic and disturbance regimes, and incorporate this knowledge into land management and restoration actions.…”