| Material cycle and energy flow is one of the most basic functions of terrestrial ecosystems.Litters is the material returned to the ground after the withering or death of above-ground plant tissues or organs,and it participates in the closed loop of material cycle of soil → plants → litters → decomposer → soil as the main material and energy source of decomposer.The study of the decomposition process of litter matter and its dynamic release pattern of nutrients and heavy metals in a specific region is of great significance for the efficient utilization of resources and ecological environmental protection.In this study,we conducted a 600-day field decomposition experiment using the decomposition bag method to investigate the decomposition process of litter and reed standing dead material of typical dominant plant species(reed and alkali pine)at different slopes(south and north slopes)and slope orientations(upper,middle and lower slopes)and the release of major nutrients(carbon,nitrogen and phosphorus)and heavy metals(chromium,copper,zinc and lead).The results of the study show that(1)The mass loss of reed,alkali mats and reed stagnant material during decomposition gradually decreased with the increase of decomposition time,and the mass loss at 600 d of decomposition was in the order of alkali mats,reed mats and reed stagnant material.The time required for 50% mass loss of reed and alkali mats was 142.08～190.51 d,and that for reed standing dead was 534.75～581.96 d.The time required for 95% mass loss of reed and alkali mats was 628.25～826.00 d,and that for reed standing dead was 2512.60～2631.11 d.The time required for 95% mass loss of reed and alkali mats was 628.25～826.00 d,and that for reed standing dead was 2512.60～2631.11 d.(2)The elemental contents of reed,alkali poncho and reed standing dead showed different trends during decomposition: the carbon content of reed and alkali poncho decomposed from 0 to 120 d,gradually increased after 120 d,and fluctuated within a certain range after 240 d.The nitrogen content of reed and alkali poncho decomposed gradually increased after decomposition began,reaching the maximum value at 240 d and 300 d,respectively.The content of carbon,nitrogen and phosphorus in reed litter gradually decreased after decomposition began.The trends of heavy metals in reed,alkali poncho and reed standing dead were basically the same,with chromium and copper contents gradually decreasing after decomposition began,zinc contents gradually increasing after decomposition began,and no significant changes in lead contents.(3)The net release rates of carbon,nitrogen and phosphorus in reed,alkali poncho and reed standing dead were 85.51%～88.87%,77.85%～83.35% and 91.84%～95.23%,respectively,and the net release rates of alkali poncho were 89.80%～92.99% after 600 d of decomposition.89.80%～92.99%,85.87%～89.57% and 94.66%～96.54%,respectively,and the net release rates of three elements from reed standing dead material were 71.26%～72.96%,67.36%～68.37% and 82.01%～82.24%,respectively.The net release rate of phosphorus was the highest and the net release rate of nitrogen was the lowest after 600 d of decomposition for both the litter and standing dead material,and the net release rate of carbon,nitrogen and phosphorus was the highest for the litter material and the lowest for the standing dead material.After 600 d of decomposition,the net release rates of chromium,copper,lead and zinc from reed and alkali ponies were 91.98%～92.10%,91.79%～91.97%,90.86%～91.04%and 88.70%～89.39%,respectively,with the release rates of chromium and lead from the lower slope of the two species of reed and alkali ponies being significantly higher than those from the middle and upper slopes,but the difference in the net release rates of each heavy metal from the south and north slopes was not significant.The net release rates of Cr and Pb were significantly higher on the lower slope than on the middle and upper slopes.The net release rates of chromium,copper,lead and zinc from reed standing dead material ranged from 66.98% to 67.53%,66.33% to 67.67%,62.31% to 63.92% and 55.05% to 57.17%,respectively,and the differences in net release rates between the south and north slopes were not significant.(4)The loss of quality and elements in litter decay process was significantly affected by environmental factors(soil salinity,moisture and temperature)in saline sites.The correlation analysis showed that soil salinity content significantly inhibited the loss of quality and elemental release of alkali mats,while the increase of soil water content reduced the inhibitory effect of soil salinity,and the influence of soil temperature on the decomposition process of alkali mats was not significant;soil temperature was the main factor affecting the decomposition of reed mats and standing dead matter,and the decomposition rate of reed mats and standing dead matter increased significantly with the increase of soil temperature.Soil temperature was the main factor influencing the decomposition of reed litter and standing dead material,while soil salinity and water content did not have significant effects on the net loss of reed litter and standing dead material quality and elements.(5)Litter decomposition and the release of elements and heavy metals did not significantly affect soil organic matter,total nitrogen,fast-acting phosphorus and heavy metal content.The contents of soil organic matter,total nitrogen,fast-acting phosphorus and heavy metals showed obvious cyclical changes during the decomposition period,among which the contents of soil organic matter and fast-acting phosphorus peaked at 180 d and 540 d of decomposition,respectively,and were lowest at 360 d of decomposition,while the contents of soil total nitrogen showed the opposite trend.The lowest content was found at 360 d. |
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