Abstract
Caragana microphylla is a sand-fixing leguminous shrub with strong resistance to drought, cold, and low soil fertility. As a result, it plays an essential role in combating desertification in northern China, but little is known about its nutrient budget. Nutrient resorption is a key process in plant nutrient conservation and has marked ecological implications for plant fitness and ecosystem nutrient cycling. We studied the effects of both nitrogen (N) addition and reproductive effort on leaf N resorption of C. microphylla in a temperate semi-arid sandy land in China. The results showed that sprouting of the early leaves from over-wintered buds employs a strategy for slow returns on nutrient investment with smaller specific leaf area (SLA) and higher N resorption efficiency, whereas the late leaves, which sprout from current-year buds, employ a strategy for quick returns on nutrient investment with higher SLA and lower N resorption efficiency. N addition significantly increased the N resorption efficiency from early leaves while exerting no impact on late leaves, suggesting that the increased N recovery from early leaves is done to sustain the high N demands of late leaves. Reproductive effort did not affect the N resorption from early or late leaves due to the temporal separation between fruit production and leaf senescence. Taken together, our results demonstrate that C. microphylla has evolved different investment strategies for leaf N in early and late leaves to conserve nutrients and facilitate its growth in desertified environments.
Highlights
Nutrient resorption in plants is the remobilization of nutrients from senescing tissues to living organs or storage structures (Aerts and Chapin, 2000)
The N concentration in green late leaves was significantly higher than that in early leaves in the N0 and N1 treatments, but there was no significant difference in the N2 treatment (Figures 4A,D)
Our experiment showed that the N resorption efficiency from early leaves of C. microphylla was between 40 and 60%, vs. less than 20% for late leaves
Summary
Nutrient resorption (retranslocation) in plants is the remobilization of nutrients from senescing tissues to living organs or storage structures (Aerts and Chapin, 2000) This process appears to be a key nutrient conservation mechanism in most plant species and in most ecosystems, as this process makes plants less dependent on nutrient availability from their environment (Wright and Westoby, 2003). It is reasonable to expect that plants that inhabit infertile environments would be more efficient at resorbing nutrients than plants that inhabit fertile environments (Li et al, 2013) This hypothesis is still being debated, as it has been supported by some studies (Killingbeck, 1993b; Wright and Westoby, 2003; Yuan et al, 2005) but contradicted by others (Killingbeck and Whitford, 2001; Wang et al, 2017).
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