分类： 地球科学 >> 地理学 提交时间： 2021-01-15 合作期刊: 《干旱区科学》
摘要： Ping′ou hybrid hazelnut is produced by cross cultivation and is widely cultivated in northern China with good development prospects. Based on a field experiment of fertilizer efficiency, the leaf spectral reflectance and leaf potassium (K) concentration were measured with different quantities of K fertilizer applied at four fruit growth stages (fruit setting stage, fruit rapid growth stage, fruit fat-change stage, and fruit near-maturity stage) of Ping′ou hybrid hazelnut in 2019. Spectral parameters that were significantly correlated with leaf K concentration were selected using Pearson correlation analysis, and spectral parameter estimation models of leaf K concentration were established by employing six different modelling methods (exponential function, power function, logarithmic function, linear function, quadratic function, and cubic function). The results indicated that at the fruit setting period, leaf K concentration was significantly correlated with Dy (spectra slope of yellow edge), Rg (reflectance of the green peak position), λo (red valley position), SDb (blue edge area), SDr/SDb (where SDr represents red edge area), and (SDr–SDb)/(SDr+SDb) (P<0.01). There were significant correlations of leaf K concentration with Dy, Rg, SDb, Rg/Ro (where Ro is the reflectance of the red valley position), and (Rg–Ro)/(Rg+Ro) at the fruit rapid growth stage (P<0.01). Further, significant correlations of leaf K concentration with Rg, Ro, RNIR/Green, and RNIR/Blue were obtained at the fruit fat-change period (P<0.01). Finally, leaf K concentration showed significant correlations with Dr, Rg, Ro, SDy (yellow edge area), and SDr at the fruit near-maturity stage (P<0.01). Through a cubic function analysis, regression estimation model of leaf K concentration with highest fitting degree (R2) values at the four fruit growth stages was established. The findings in this study demonstrated that it is feasible to estimate leaf K concentration of Ping′ou hybrid hazelnut at the various phenological stages of fruit development by establishing regression models between leaf K concentration and spectral parameters.
分类： 环境科学技术及资源科学技术 >> 环境科学技术基础学科 提交时间： 2019-12-06 合作期刊: 《干旱区科学》
摘要： Forest recovery may be influenced by several factors, of which fire is the most critical. However, moderate- and long-term effects of fire on forest recovery are less researched in Northwest China. Thus, the effects of different forest recovery time after fire (1917 (served as the control), 1974, 1983 and 1995) and fire severities (low, moderate and high) on larch (Larix sibirica Ledeb.) forest were investigated in the Kanas National Nature Reserve (KNNR), Northwest China in 2017. This paper analyzed post-fire changes in stand density, total basal area (TBA), litter mass, soil organic carbon (SOC) and soil nutrients (total nitrogen, total phosphorus and total potassium) with one-way analyses of variance. Results indicate that litter mass, TBA, SOC and soil nutrients increased with increasing recovery time after fire and decreasing fire severity, while the stand density showed an opposite response. The effects of fire disturbance on SOC and soil nutrients decreased with increasing soil depth. Moreover, we found that the time of more than 43 a is needed to recover the litter mass, TBA, SOC and soil nutrients to the pre-fire level. In conclusion, high-severity fire caused the greatest variations in stand structure and soil of larch forest, and low-severity fire was more advantageous for post-fire forest stand structure and soil recovery in the KNNR. Therefore, low-severity fire can be an efficient management mean through reducing the accumulation of forest floor fuel of post-fire forests in the KNNR, Northwest China.
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