Effects Of Mowing And Nutrient Addition On Plant Phenology Of Typical Steppe In Inner Mongolia

Phenology is the periodic events modulated by plants according to seasonal and environmental,especially temperature changes.Plant phenological variation has significance to plant growth,reproduction and species coexistence in communities.Phenological events are ideal indicators of the impact of environmental and human disturbance on plant community succession and ecosystem functioning.Mowing for hay is an important human activity in Inner Mongolia grasslands.Nutrient deficiency widely limits plant growth in temperate grasslands.Mowing prevents nutrient returning and changes microenvironmental conditions by removing aboveground vegetation,but the impact on plant phenology and the mechanism by which different plant species modulate their growth are unclear.We conducted a manipulative field experiment involving nutrient addition and mowing in a temperate steppe in Inner Mongolia.We investigated vegetative and reproductive phenology and fast-growth traits for four common species Leymus chinensis,Stipa krylovii,Cleistogenes squarrosa,and Thalictrum petaloideum.Structural-equation model(SEM)was used to analyse the way of mowing and nutrient addition to plant phenological traits.The findings indicated that mowing led to earlier onset of leaf developing and flowering by 3 to 8 days for L.chinensis,S.krylovii,C.squarrosa,while had less impact on the onset of leaf developing for T.petaloideum.The period for vegetative growth of L.chinensis and C.squarrosa became shorter under mowing.The phenological traits during vegetative growth phases did not respond to nutrient enrichment.The responses of reproductive phenology to mowing varied among species.An earlier flowering and fruiting time for L.chinensis led to unchanged flowering period under mowing.The onset of flowering for S.krylovii and C.squarrosa advanced 2 to 13 days after mowing;but the delayed flowering and fruiting time shortened the whole flower duration for T.petaloideum.The four species during reproductive phenological phase responded weakly to nutrient availability.Studying plant species fast-growth demonstrated different impact of mowing and nutrient addition.The increase of nutrient availability is likely to alleviate the negative impact of mowing on plant growth.The SEM analysis showed that soil temperature triggered the changing of plant phenology of herbaceous plants by direct and indirect impacts.During the earlier period of plant growth,lower soil temperature after mowing shortened the vegetative growth without delaying leaf development.When reproductive tissues emergence,increasing soil temperature by mowing advanced graminoid plants directly or indirectly through inhibiting plant height.The thesis demonstrated that long-term mowing has stronger impacts on phenological traits and life cycling for grassland herbaceous species than nutrient addition,through altering soil temperature.However,the responses of phenological traits commonly vary greatly among species.The difference in plant phenology may allow species coexistence under the environmental change or disturbance.Studying phenology of different plants can be further used for understanding of the consequence of global change and human activities on community succession and ecosystem functions in grasslands.