Reduced release of labile carbon from Abies fargesii var. faxoniana needle litter after snow removal in an alpine forest

doi:10.17521/cjpe.2022.0111

Abstract

Abstract:

Aims Changes in the depth and duration of seasonal snowpack induced by climate change may affect litter decomposition, particularly the release of labile carbon during the early decomposition periods in alpine forests. Our objective of this study was to assess the effect of snow removal on labile carbon fractions in litter (i.e., dissolved organic carbon (DOC), hot-water extractable carbon (HWEC) and non-structural carbon (NSC)) during early stage of litter decomposition in an alpine forest on the eastern Qingzang Plateau.
Methods An in situ litter input microcosm experiment was conducted in an alpine forest dominated by 120 to 150-year-old fir (Abies fargesii var. faxoniana) from October 2018 to October 2019. Air-dried fir needle litter was incubated at control and snow removal plots and the concentrations of total organic carbon (TOC), DOC, HWEC, NSC, soluble sugars and starch in decomposing fir litter were determined during winter (snow formation period, snow coverage period and snow melt period) and growing season (early, middle and late growing season).
Important findings Results showed that litter mass remained by 76.4% and 86.2% at control and snow removal plots, respectively, over one year of decomposition. After decomposition for one year, 60.5% and 74.8% of organic carbon remained in decomposing litter at control and snow removal plots, respectively. After decomposition for a winter, the release of HWEC and soluble sugars from decomposing litter were lower, while TOC, DOC, NSC and starch in fir needle litter were higher in snow removal plots than that in control plot. After decomposition for a growing season, the release of TOC, HWEC, DOC, NSC, soluble sugars and starch were reduced by 36.3%, 0.8%, 43.7%, 28.3%, 21.7% and 33.7%, respectively, in the snow removal plots compared to those in the control plots. The results from partial least square model indicated that labile carbon release was strongly controlled by soil freezing-thawing cycle, urease activity, soil temperature and DOC concentration. These results suggest that the presence of snow cover accelerated the release of labile carbon from decomposing litter during winter and growing seasons, highlighting the importance of seasonal snow cover in controlling litter decomposition in high-latitude and high-altitude ecosystems. Moreover, the significant influence of snow cover on labile carbon release during winter could have a legacy effect on litter decomposition during the subsequent growing season, suggesting that snow cover is of great significance for soil biogeochemical cycles in this alpine forest.

Key words: snow removal, needle litter decomposition, labile carbon, non-structural carbon, alpine forest

LAI Shuo-Tian, WU Fu-Zhong, WU Qiu-Xia, ZHU Jing-Jing, NI Xiang-Yin. Reduced release of labile carbon from Abies fargesii var. faxoniana needle litter after snow removal in an alpine forest[J]. Chin J Plant Ecol, 2023, 47(5): 672-686.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0111

https://www.plant-ecology.com/EN/Y2023/V47/I5/672

Figures/Tables 12

Fig. 1 Changes in environmental factors in an alpine forest on the eastern Qingzang Plateau during the study period. A, Snow depth. B, Soil surface temperature. C, Daily mean temperature of soil organic layer. D, Gravimetric water content in decomposing litter. Values are mean ± SE (n = 5) in A, C and D. p shows results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods, and asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01; ***, p < 0.001). EG, early growing season period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Table 1 Number of freeze-thaw cycles of soil organic layer in the control and snow removal plots in an alpine forest on the eastern Qingzang Plateau

分解时期 Decomposition period	对照 Control	雪被去除 Snow removal
雪被形成期 Snow formation period	13	16
雪被覆盖期 Snow coverage period	6	3
雪被融化期 Snow melt period	5	31
生长季初期 Early growing season period	0	0
生长季中期 Middle growing season period	0	0
生长季后期 Late growing season period	1	3

Fig. 2 Effects of snow removal on mass of Abies fargesii var. faxoniana needle litter during the study period (mean ± SE, n = 5). p in A shows results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods and asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; ***, p < 0.001). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Table 2 Regression equation, correlation coefficient, decomposition coefficient, 50% and 95% decomposition time of leaf litter of Abies fargesii var. faxoniana in snow removal and control plots (mean ± SE, n = 5)

处理 Treatment	回归方程 Regression equation	相关系数 Correlation coefficient (R²)	分解速率 Decomposition rate (a^-1)	50%分解时间 Time of half decomposition (a)	95%分解时间 Time of 95% decomposition (a)
对照 Control	y = 101.3e^-0.264^x	0.956 ± 0.021	0.266 ± 0.033^a	2.60 ± 0.281^b	11.25 ± 1.22^b
雪被去除 Snow removal	y = 99.5e^-0.134^x	0.934 ± 0.013	0.134 ± 0.006^b	5.17 ± 0.233^a	22.32 ± 1.01^a

Fig. 3 Effects of snow removal on total organic carbon (TOC) in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01; ***, p < 0.001). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Fig. 4 Environmental factors in explaining labile carbon during litter decomposition of Abies fargesii var. faxoniana (mean ± SE). A, Partial least squares (PLS) coefficient. PLS coefficients greater than 0 show positive effect and those less than 0 show negative effect. Red indicates that the variable had a significant effect (p < 0.05). B, Variable importance. The values greater than 1 represent significant effect (p < 0.05, red). DMT, daily mean temperature in soil organic layer; DOC, dissolved organic carbon concentration in soil organic layer; DON, soil dissolved organic nitrogen concentration; Invertase, soil invertase activity; MBC, microbial biomass carbon concentration; MBN, microbial biomass nitrogen concentration; Microbial Res, microbial respiration rate; NFTC, soil freeze-thaw cycle; NH4+, Soil NH4+ concentration; NO3-, soil NO3- concentration; Snow, snow depth; Soil moisture, soil organic layer moisture; Urease, soil urease activity.

Fig. 5 Correlations between litter labile carbon of Abies fargesii var. faxoniana and environmental factors. A, Control; B, Snow removal. DMT, daily mean temperature in soil organic layer; DOC, dissolved organic carbon concentration of needle litter; HWEC, hot water-extraction carbon concentration; MBC, microbial biomass carbon concentration; MBN, microbial biomass nitrogen concentration; Microbial Res, microbial respiration rate; NFTC, soil freeze-thaw cycle; NO3-, soil NO3- concentration; NSC, non-structural carbon concentration; Snow, snow depth; Soil DOC, dissolved organic carbon concentration in soil organic layer; Soil moisture, soil organic layer moisture; Starch, starch concentration; Sugar, soluble sugar concentration; TOC, total organic carbon concentration; Urease, soil urease activity; Water, water content of litter. Asterisks denote significant correlations between variables (*, p < 0.05; **, p < 0.01).

Fig. 6 Effects of snow removal on hot water-extraction organic carbon (HWEC) in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Fig. 7 Effects of snow removal on dissolved organic carbon (DOC) in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01; ***, p < 0.001). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Fig. 8 Effects of snow removal on non-structural carbon (NSC) in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Fig. 9 Effects of snow removal on soluble sugar in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01; ***, p < 0.001). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

Fig. 10 Effects of snow removal on starch in litter of Abies fargesii var. faxoniana during the decomposition period (mean ± SE, n = 5). p in A and B show results from repeated measures ANOVA testing for the effect of snow removal in different decomposition periods. Asterisks denote significant differences between control and snow removal plots based on t-test (*, p < 0.05; **, p < 0.01; ***, p < 0.001). EG, early growing season period; Initial, initial period; LG, late growing season period; MG, middle growing season period; SC, snow coverage period; SF, snow formation period; SM, snow melt period.

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