Grazing increases evapotranspiration without the cost of lowering soil water storages in arid ecosystems

Abstract

Grazing is the predominant land use practice in arid environments; however, there are relatively few studies of grazing effects on ecosystem functioning. We assessed the impact of grazing on soil moisture, evapotranspiration (ET), canopy conductance (Gc), and root water uptake in the Patagonian steppe. Studies were done in 3 sites along a gradient of grazing intensity. High grazing intensity increased the soil water storage by 24% and decreased the amount of water extracted from deep layers compared to the low grazing intensity. Grazing affected ET and its partitioning into transpiration (T) and evaporation. High shrub cover and Gc increased ET and T or ET partitioning in the heavily grazed site. Annual ET increased from 78% to 92% of the annual precipitation from the lowest to the highest grazing intensity, respectively. Total T was 21% higher in the highest intensity site compared to the lowest intensity site. Changes in Gc suggest that grazing modified the canopy architecture, and thus the response of vegetation to environmental factors. At the beginning of the growing season when moisture was high, Gc exhibited the highest value in the heavily grazed site, but a strong regulation of water losses was observed under drier conditions. This study emphasizes the need to assess simultaneously multiple factors for understanding regulatory mechanisms of grazing effects on hydrological processes. From a sustainable management point of view, we suggest that increasing the number of water sources, and thus spreading the sheep in a paddock, can enhance the stocking rate while maintaining soil water storage.

Controls of Temporal Variations on Soil Respiration in a Tropical Lowland Rainforest in Hainan Island, China

“…The decrease in soil water availability during the dry season affects several physiological processes, leading to plant dehydration and a substantial loss of root functionality in this ecosystem (Bucci et al., 2013; Scholz et al., 2012). This was also reflected in a decrease in plant transpiration during the drought period (Pereyra et al., 2017), and hence a decrease in CO 2 capture. Furthermore, at low soil moisture conditions, decomposition is limited by soluble C availability (Davidson et al., 2012; Linn & Doran, 1984).…”

Soil Respiration and N-Mineralization Processes in the Patagonian Steppe Are More Responsive to Nutrient Than to Water Addition

“…An increase in underground biomass with N and P addition has been previously reported in other ecosystems (Li et al 2015;Huang et al 2018). It should be noted that we only evaluated the effects of the treatments on root biomass in the rst 10 cm depth, but in this ecosystem more than 40% of roots are found in this soil layer and less than 20% at 50 cm depth (Pereyra et al 2017). Moreover, the ne roots located in the upper part of the soil pro le have higher rates of respiration than larger roots or the few roots located deeper in the soil (Pregitzer et al 1998).…”

Ojos que no ven... ¿Qué podemos hacer para incluir más a la fracción subterránea en estudios de vegetación?

“…Por último, el 8% de los estudios evaluó la tasa de descomposición radical (Tabla 1). Si bien la estimación de la BS parece ser la principal variable de estudio, es necesario obtener otras variables complementarias que permitan determinar cómo las plantas responden a distintos factores ambientales en diferentes ecosistemas y cuál es la profundidad de enraizamiento o la de captación de agua por parte de las raíces (Bucci et al 2009;Pereyra et al 2017).…”