A nurse shrub species helps associated herbaceous plants by preventing shade‐induced evaporation in a desert ecosystem

Abstract

Xeric shrubs often play an important role in reversing desertification and promoting ecological restoration of degraded dryland ecosystems. However, how shrubs affect their associated herbaceous species and environmental conditions remains largely unknown. In this study, we conducted a removal experiment along with stable isotope analysis to determine the water use strategy of a shrub species (Artemisia ordosica) and its associated perennial graminoids (PG) in the Mu Us Desert, northern China. We observed that in the intact plots, both shrubs and PG predominantly utilized water from the shallow soil layer (0–20 cm, 54.36%, and 63.63%, respectively). Compared to this, when shrubs were removed, soil water content decreased, the main water source of PG switched to the middle soil layer (20–60 cm, 48.25%), and their water use efficiency (WUE) increased. However, the removal of PG had no significant impacts on the soil water content in any layer or on the water source of shrubs but for slightly decreased WUE. We highlighted that rather than hydraulic lift, shade‐induced evaporation decline is the primary mechanism by which shrubs facilitate the growth of associated herbaceous plants in desert ecosystems, indicating that the facilitated herbaceous plants have more flexible water use strategies than shrubs, which probably drives the community succession from being shrub‐dominated to herb‐dominated.

Shrub-mediated effects on soil nitrogen determines shrub-herbaceous interactions in drylands of the Tibetan Plateau

“…We found soil moisture underneath the shrub canopy was generally lower than that in the open area (Supplementary Figure 1), also the water availability indicator, leaf d 13 C of grasses, was slightly higher within C. versicolor canopies than outside at most study sites across the water gradient, suggesting that shrubs do not increase soil moisture as do in other facilitator species (Prieto et al, 2011;Tirado et al, 2015;Liu et al, 2021). Water availability is the most important factor limiting plant survival in dry regions, where increasing water availability translates into increased plant survival (Liancourt et al, 2005).…”

“…Considering different functional groups, we found that C. versicolor increased grass species richness but had a negative effect on forbs. The higher competitive ability of grasses compared to other functional groups has been shown in several experiments (Maestre and Cortina, 2004;Noumi et al, 2015;Liu et al, 2021) due to its higher root investment and resources uptake abilities (Gómez-Aparicio, 2009;Gross et al, 2009;Michalet et al, 2015). In addition, exclusion of forbs by C. versicolor could be also due to the generally high N demand of forbs, resulting in strong competition between forbs and shrub for N.…”

“…Shrubs often act as nurse plants in arid habitats where water availability and soil nutrients are limiting factors (Butterfield et al, 2016), increasing species diversity (O'Brien et al, 2019) through buffering environmental conditions, increasing resource availability and/or protecting against herbivores (Maestre et al, 2009;Tirado et al, 2015;Zhang et al, 2018a). Shrubs could increase soil water availability through hydraulic lift (Richards and Caldwell, 1987;Prieto et al, 2011) or shading effect (Liu et al, 2021). However, shrubs can also have negative effects on soil water content mostly through interception loss in shrub canopies and enhanced utilization of soil water (Tielbörger and Kadmon, 2000;Darrouzet-Nardi et al, 2006;Hamerlynck et al, 2011).…”

Goldilocks forbs: survival is highest outside—but not too far outside—of Wyoming big sagebrush canopies

“…Previous research has found that in postfire restoration settings commonly encountered in this region, remnant, dead sagebrush canopy microsites can greatly increase survival of both transplanted woody and seeded herbaceous species (Boyd & Davies 2010; Davies et al 2017, 2020). However, in intact, unburned semiarid systems, aboveground canopy ameliorations are considered more influential than belowground resource availability on seedling survival (Gómez‐Aparicio et al 2005; Liu et al 2021). In the Intermountain West, intact systems are also more likely to be characterized by intact biological soil crust (BSC) communities which can increase (or decrease) establishment and by lower invasive annual grass cover which can improve plant establishment (Bradley et al 2018; Havrilla et al 2019; Condon & Gray 2020).…”

Under drought conditions, fungicide seed coating does not increase emergence of two native grass species in sagebrush stands of the Intermountain West, U.S.A.

“…Interactions within microbial communities and with their environment influence seedling viability in complex ways (Lamichhane & Venturi 2015; Lamichhane et al 2018), but there is evidence that higher soil moisture increases the detrimental effects of fungal pathogens on seed viability (Mackin et al 2021). As such, although the favorable hydrothermal conditions in shrub canopy microsites can improve seedling establishment (Davies et al 2007; Liu et al 2021), the higher soil moisture may also increase susceptibility of seeds to fungal pathogens. Therefore, combining the two approaches may allow seeds to benefit from the positive canopy microenvironment, while offsetting any negative effects of potentially higher levels of fungal pathogens.…”