Sulfur Cycling In Plant-soil System Influenced By The Invasion Of Spartina Alterniflora In The Min River Estuary

An estuarine wetland acts as a critical zone which is well known as a sensitive response indicator to globl changes and regional environmental problems and a habitat type easily invaded by foreign plants as well.At present,studies on the bioelement cycling of the estuarine wetlands by the invasion of Spartina alterniflora mainly focus on the charactristics and influencing factors of carbon and nitrogen nutrient cycling,soil sulfur distribution,as well as plant ecological traits residual decomposition,nutrient dynamics,etc.,.However,studies involved in the characteristics of sulfur cycling in plant-soil?water?systems for the S.alterniflora invasion are still very limited,especially for studies of the sulfur cycle in wetlands under the invasion time series of S.alterniflora.To determine the effect of S.alterniflora invasion on sulfur cycling characteristics in plant-soil system in the Min River estuary,a total of 9 plots of S.alterniflora invasive vegetation types occured in different years were selected using the space-for-time substitution method.The main research results were given as follows:?1?Soil sulfur storage of bare flat?BF?,S.alterniflora-bare flat?SA?BF??community and S.alterniflora?HSA?community were 658.74±29.63 g S·m^-2,604.30±49.80 g S·m^-2and 525.54±20.04 g S·m^-2,respectively.Soil sulfur storage significantly decreased with the invasion of S.alterniflora?P<0.05?.The pore water sulfur storage in different stages of S.alterniflora invasion showed SA?BF?>BF>HSA?P<0.05?,and the pore water sulfur storage decreased after S.alterniflora invasion,which may be related the shifts of the soil particle size caused by the invasion of S.alterniflora.The changes in soil particle size and plant types due to invasion of bare flat by S.alterniflora were the key drivers of sulfur content distribution.Under the conditions of aerobic and anaerobic,the soil sulfur accumulation mineralization amount of BF was higher than that of SA?BF?and HSA?P<0.05?.The plant sulfur storage of SA'BF'and HSA were 5.66±1.48 g·m^-2and 5.71±1.59 g·m^-2,respectively.The sulfur storage ratio of stems and roots of HSA was higher than that of SA'BF',while the sulfur storage ratio of leaves,sheaths and ears were lower than SA'BF'.The S.alterniflora invasion significantly increased the sulfur storage of the plants and the return of sulfur nutrients from the residues.?2?The S.alterniflora invasion Cyperus malaccensis reduced the sulfur storage of wetland soil.The sulfur storage of soil of C.malaccensis?CM?community was 1.06 time that of S.alterniflora-bare flat?CM?SA??community and 1.14 time that of S.alterniflora community?P>0.05?.The pore water sulfur storage in different stages of S.alterniflora invasion were between 77.97?257.88 g SO₄^2-·m^-2?CM?,96.61?241.23 g SO₄^2-·m^-2?CM?SA??and 89.51?229.61 g SO₄^2-·m^-2?SA?,respectively.Under the aerobic condition,the sulfur accumulation mineralization amount of CM?SA?was 1.29?1.35 time and1.89?2.30 time that of CM and SA?P<0.05?,while under anaerobic condition,the sulfur accumulation mineralization amount of SA was greater than that of CM?SA?and CM?P<0.05?.In the process of competition between C.malaccensis and S.alterniflora,the C.malaccensis focused on the distribution of sulfur nutrients in the underground part and enhanced the underground space to maintain competitiveness.Sulphur nutrient distribution of S.alterniflora seemed more inclined to aboveground organs to enhance the ability to capture light and improve the competitive advantage on the ground.Plant sulfur storage increased significantly by 17.4%after the invasion of S.alterniflora.The matrix quality of the plant residue and the physical and chemical properties of the soil changed significantly,reducing the decomposition rate and nutrient release intensity of the residues.In the early stage of the invasion of S.alterniflora,the invasion advantage of S.alterniflora exacerbated by absorbing and utilizing large amounts of nutrients returned from the residues of C.malaccensis.?3?The soil sulfur storage in different S.alterniflora invasion years were shown as follows:2?6 years of S.alterniflora invasion(SA₆:525.54±40.08 g S·m^-2)>6?10 years of S.alterniflora invasion(SA₁₀:511.53±61.76 g S·m^-2)>10?14 years of S.alterniflora invasion(SA₁₄:451.40±27.52 g S·m^-2)?P<0.05?.The soil sulfur storage reduced significantly by 14.11%with the increase of the invasive years of S.alterniflora.Compared with bare flat,the sulfur storage of pore water of SA₆,SA₁₀ and SA₁₄decreased by 7.20%,6.22%and 11.24%,respectively.Sulfur accumulation mineralization amount of SA₁₄ was 0.86?1.36 time of SA₆and 1.02?1.12 time of SA₁₀?P<0.05?,and the cumulative mineralization amount of soil sulfur increased with the increase of invasive years of S.alterniflora.The sulfur storage of S.alterniflora in different invasion years were expressed in SA₁₄(8.82±1.46 g·m^-2)>SA₁₀(7.49±1.12g·m^-2)>SA₆(5.71±1.59 g·m^-2).With the extension of invasion years,plants biomass increased and more sulfur was requried for plant growth,thus plant sulfur reserves increased significantly.Whereas,the sulfur storage distribution ratio of S.alterniflora root decreased with the increase of invasion years,and the sulfur nutrients supplied to the aboveground parts increased obviously.?4?Overall,the invasion of S.alterniflora significantly changed the sulfur cycle of the plant-soil system in the Min River estuary,but the sulphur nutrient allocation strategies for invasion adopted by S.alterniflora under different habitat types and in different invasive years were different.When S.alterniflora invaded the bare flat,it was inclined to distribute more sulfur nutrients to the underground organs?roots?to enhance the absorption and utilization of sulfur nutrients in the roots.The sulphur nutrient allocation strategis adopted by S.alterniflora when invading C.malaccensis communities were different from that when invading the bare flat.The sulphur nutrients supplied to the aboveground parts of S.alterniflora increased significantly,making it dominant in the competition of space and light resources,inhibiting the growth of aboveground organs of C.malaccensis,and thus occupying an advantage in the competition.With the increase of the invasion years of S.alterniflora,the investment of the underground part was relatively reduced,while the investment of the aboveground part was relatively increased.Such a sulfur nutrient distribution strategy can not only enhance the capture of light resources to improve the primary productivity,but also be conducive to the survival and development of the population.