Tradeoffs between nitrogen- and water-use efficiency in dominant species of the semiarid steppe of Inner Mongolia

Abstract

In water-limited environments, photosynthetic carbon gain and loss of water by transpiration are in a permanent tradeoff as both are contrarily regulated by stomata conductance. In semiarid steppe grasslands water limitation may covary with nitrogen limitation. Steppe grassland species are capable of optimizing their use of limiting resources, water and nitrogen, but regulation is still poorly understood. In a two-year experiment with addition of water (irrigation simulating a wet year) and nitrogen (0, 25, and 50 kg urea-Nha −1 ) we assessed intrinsic water use efficiency (WUE i ), nitrogen use efficiency (NUE), and related plant functional traits (PFTs) of four dominant C 3 species (Leymus chinensis, Agropyron cristatum, Stipa grandis, and Artemisia frigida). Water and N fertilizer supplementation significantly increased plant primary production, and N effect was more pronounced under irrigated conditions. Parallel with the responses of plant production, a strong tradeoff between WUE i and NUE was detected: water supply increased NUE but decreased WUE i , whereas N addition slightly increased WUE i at the expense of NUE. This tradeoff occurred at the leaf level, and involved the responses of leaf N concentration and specific leaf area. WUE i of species changed among treatments in a predictable manner by the parameter of leaf N content per area. Dominant plant species commonly achieved a higher utilization efficiency of the more limiting resource via altering PFTs, which was an important mechanism of adaptation to variable resource limitation in semiarid grasslands.

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales

“…Caldeira et al, 2001). For example, in a tropical rainforest, 13 C was associated with differences in shade tolerance (Bonal et al, 2000;Guehl et al, 2004), whereas in an upland water-limited grassland of Greece, a semi-arid Inner Mongolian steppe, and a Portuguese mediterranean macchia grouping according to 13 C was associated with species' competitive ability related to WUE i , nitrogen use efficiency, and structural adaptations to drought (Tsialtas et al, 2001;Gong et al, 2010;Werner and Máguas, 2010).…”

Bundle-sheath leakiness and intrinsic water use efficiency of a perennial C4grass are increased at high vapour pressure deficit during growth

“…As ϕ is related to WUE i (Eqn 2) and potentially driven by environmental factors, we were interested to unravel the mechanisms governing Δ in this C 4 species. Furthermore, understanding the physiological response of C. squarrosa to N nutrition and VPD may provide new insight into the adaptation of this species to its habitat given that: (i) water and N availability are the major limiting factors that determine primary production and resource use efficiency of plants in the semiarid steppes of Inner Monglia (Gong et al , 2011) and (ii) the abundance of C 4 plants has increased substantially during the past several decades in the Mongolian plateau (Wittmer et al , 2010). Given the lack of knowledge on long-term effects of VPD or N nutrition and short-term dynamic effects of CO 2 on ϕ , we performed controlled environment experiments with C. squarrosa grown under a low or high level of VPD combined with a low or high level of N fertilizer supply.…”

Effects of nitrogen and vapour pressure deficit on phytomer growth and development in a C4 grass

“…Due to the dominance in many grassland types, especially degraded grasslands, C. squarrosa is considered as a key species for sustainable grassland and livestock management in this area (Liang et al 2002). In Inner Mongolian grasslands, water and nitrogen are the primary limiting factors for plant growth (Bai et al 2008); furthermore, interaction effects of N and water strongly influences physiology and morphology of dominant species (Gong et al 2011). Moreover, soil properties exhibit strong spatial heterogeneity in nitrogen and other resources due to the inattentively managed grazing activities, e.g.…”