Response of net primary productivity to precipitation exclusion in a savanna ecosystem

Abstract

Declines in precipitation are expected to affect plant performance and ecosystem carbon uptake. The response of ecosystem productivity to declines in precipitation and potential underlying mechanisms have been well studied in many biomes; however, little is known about the role of declines in precipitation and the involved mechanisms in savanna ecosystems. In a 4-year field precipitation manipulation experiment, we simulated four levels of precipitation exclusion (control, 30%, 50% and 70%) to assess the effects of declines in precipitation on net primary productivity (NPP) in a savanna ecosystem in southwestern China. NPP was strongly correlated with soil water content during the experimental period. Precipitation exclusion significantly decreased the NPP of the entire vegetation including trees, shrubs, perennials and litterfall but significantly increased the NPP of annuals. Our results suggested that precipitation exclusion can reduce the productivity of savannas and that plant functional types differ in sensitivity to precipitation exclusion. These findings imply that future declines in precipitation in savanna regions may negatively impact carbon accumulation and may induce shifts in plant functional types to buffer the effects of declines in precipitation on productivity and stabilize ecosystem function in savannas.

Impact of Tillage and Crop Residue Management on the Weed Community and Wheat Yield in a Wheat–Maize Double Cropping System

“…These findings suggest that the broadleaf weeds (forbs and legumes) may be resistant to drought due to different root systems [57,58]. The graminoids belong to the shallower-and fibrous-rooted species, whereas other weeds showed a taproot [59]. The shallower and fibrous roots of graminoid weeds may limit their ability to utilize deeper soil water, while the taproot forbs can obtain water from much deeper soil layers, which helps their survival in drought conditions [60,61].…”

Droughts and the ecological future of tropical savanna vegetation

“…Even if ecosystem productivity is regained quickly following return to normal conditions (Walker et al, ; Hoover et al, ), compositional shifts in tree and grass communities can have longer term impacts on savanna function. Severe droughts coupled with intense grazing can cause transitions from communities dominated by palatable, perennial grasses to systems composed of unpalatable, annual grasses and forbs (Fuhlendorf et al, ; Fuhlendorf & Smeins, ; Jin et al, ; Scholes, ; O'Connor, ; ). Such changes in understory composition can be particularly hard to reverse, with recovery times ranging from a few years to over a decade or more, and potentially requiring the provisioning of seeds (Fuhlendorf & Smeins, ; O'Connor, ; Walker et al, ).…”

Precipitation reduction alters herbaceous community structure and composition in a savanna

“…Drought can affect the height and cover of the herbaceous community by impacting the plant growth and species recruitment (Canham & Murphy, ; Weltzin & McPherson, ). In particular, the growth rate (net primary productivity) of the herbaceous community in this savanna dramatically decreased under 30% precipitation reduction during the study period (Jin, Li, Liu, Liu, Zhang, Song, et al., ), causing the decrease in height and cover. Moreover, precipitation reduction apparently changed the abundance of different plant functional groups in the present study (Figures and ), disproportionately depressing the abundance of the most dominant groups (e.g., graminoids and perennials), indicating that declines in precipitation could affect the density and species recruitments of the herbaceous community and then lead to decreased community cover and height.…”

“…These findings suggest that forbs and legumes may be more resistant to drought due to different root traits (Chelli et al., ; Mulhouse, Hallett, & Collins, ; Tetetla‐Rangel, Dupuy, Hernández‐Stefanoni, & Hoekstra, ). The graminoids in this savanna ecosystem belong to the shallower‐ and fibrous‐rooted species, whereas the forbs and legumes belong to taproot species (Jin et al., ; Jin, Li, Liu, Liu, Zhang, Song, et al., ). The shallower and fibrous roots for graminoids may limit their ability to access deeper soil water following a reduction in surface soil water and increased overstorey and intraspecific competition (Collins & Bras, ).…”

“…Three 1 m × 1 m herbaceous quadrats were randomly placed in the interior (9 m × 9 m) of each experimental plot to limit edge effects. Biotic data were collected once a year (2014–2017) in late October, when the most of grass species in this region could be reliably identified and reached their maximum growth (Jin, Li, Liu, Liu, Zhang, Song, et al., ). For all herbaceous species, we recorded the name, abundance (number of rooted individuals), height (cm; determined by mean value of natural height from three to five individuals) and percentage cover (%).…”