Abstract
This study aimed to determine how specific leaf area (SLA) and leaf dry matter content (LDMC) respond to N addition and understory vegetation removal in a 13-year-old Mongolian pine (Pinus sylvestris var. mongolica) plantation. Traits (SLA, LDMC, individual needle dry weight, N and P concentrations) of different-aged needles and their crown-average values were measured, and their relationships with soil N and P availability were examined. N addition and understory removal reduced soil Olsen-P by 15–91%. At the crown level, N addition significantly reduced foliar P concentration (by 19%) and SLA (by 8%), and elevated N concentration (by 31%), LDMC (by 10%) and individual leaf dry weight (by 14%); understory removal did not have a significant effect on all leaf traits. At the needle age level, traits of the previous year’s needles responded more strongly to N addition and understory removal than the traits of current-year needles, particularly SLA and N concentration. SLA and LDMC correlated more closely with soil Olsen-P than with soil inorganic N, and LDMC correlated more closely with soil Olsen-P than SLA did. These results indicate that aggravated P limitation resulting from N addition and understory removal could constrain Mongolian pine growth through their effects on the leaf traits.
Highlights
Enhanced nitrogen (N) deposition and the elimination of understory vegetation are two of the main drivers that affect soil nutrient availability in managed forests, and the altered nutrient availability has great potential to change the ecosystem structure and functioning
We examined the morphological traits and nutrient concentrations of different-aged needles and soil physiochemical properties and analyzed their correlations in a pure Mongolian pine (Pinus sylvestris var. mongolica) plantation that has been subjected to five years of N addition and understory removal
Soil Olsen-P was reduced by both N addition and understory removal in the Mongolian pine plantation, with a stronger effect of N addition (Table 1)
Summary
Enhanced nitrogen (N) deposition and the elimination of understory vegetation are two of the main drivers that affect soil nutrient availability in managed forests, and the altered nutrient availability has great potential to change the ecosystem structure and functioning. Considering that climate change and human disturbances have substantially altered nutrient availability and cycles[1, 21], understanding how the variation in nutrient availability affects SLA and LDMC is urgent for predicting the dynamics of ecosystem functioning in a changing world. Most previous studies on the leaf traits of Pinus only measured the current-year needles without considering the previous year’s needles, despite old needles possibly being more sensitive to variations in soil nutrient availability than new needles due to the transfer of nutrients from old to new leaves[32]. The overall goal of this study was to determine how variations in soil N and P availability, induced by N addition and understory vegetation removal, affect foliar chemistry and morphology in a nutrient-poor Mongolian pine plantation. Given that Mongolian pine is one of the most widespread tree species planted at infertile sites with low N and P availability in northern China[34, 35], the results of the present study can provide useful information for simulating and predicting the growth and adaptation responses of pine stands to variations in nutrient availability induced by climate change and artificial disturbances
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