Nutrient Physiology Of Betula Ermanii And Picea Jezoensis And Their Responses To Altitudes In The Changbai Mountains

Alpine treeline is a sensitive ecotone in response to climate change and human activities.With global warming,upward shifts of alpine treeline have been observed areas around the world,while some drought-prone areas have seen unchanged or even downward shift.However,treelines may comprise of different tree species with varying responses to climate changes.As a result of the asynchrony of alpine treeline shift and climate change,an enormous challenge is to predict future alpine treeline shift,which is also one of the hot spots in the study of treeline response to climate change.Treeline in Changbai Mountain is located in high latitude and altitude areas in northeast China and is sensitive to climate change.On the west side of Changbai Mountain,the distribution of the deciduous broad-leaved Betula ermanii is from1700 m to 2200 m a.s.l.,while the distribution of the evergreen conifer Picea jezoensis is from 1100 m to 1800 m a.s.l.With climate warming,the upper limits of their distribution shift up by varying degrees.Because of the physiological differences between deciduous broad-leaved and evergreen conifer tree species,treeline ecotone in Changbai Mountain provides an ideal region for us to study these different treeline species to environmental changes.Therefore,we selected P.jezoensis and B.ermanii,the treeline species,naturally occurred in Changbai Mountain,and measured the concentrations of NSC,N,P and K of all tissues along the elevation gradient,to explore the adaptive strategy of different tree species in the harsh mountain environments.The results are as follows:(1)Carbon storage and utilization strategies of different tree species were different in the harsh mountainous environment.The concentrations of NSC,soluble sugar and starch in one-year-old leaves of P.jezoensis did not decrease with elevation,while NSC,soluble sugars and starch concentration in the leaves of B.ermanii decreased with elevation.Moreover,the starch concentration of B.ermanii shoots,stems and fine roots remained at a high level regardless of whether the soluble sugars concentration decreased.Whereas the concentrations of soluble sugars and starch in one-year-old leaves,shoots and stems of P.jezoensis responded similarly to changes with elevation.Compared with P.jezoensis,B.ermanii,as a dwarf tree species,not only has a higher soluble sugars/starch ratio and its shoots,stems and fine roots actively store NSC,but change its morphology to adapt to the harsh environment,which is one of the reasons that B.ermanii can be distributed at higher altitudes.(2)The sensitivity of nutrient physiology of different tree species to environmental changes is different.The N and K concentration in one-year-old leaves and shoots of P.jezoensis showed bimodal changes with elevation,while the N,P and K concentration in all tissues of B.ermanii presented monotonous or unimodal changes.The change of the concentrations of N,P and K in tree tissues with altitude reflected the physiological characteristic.The more complex trend indicates the greater influence of altitude.Compared with P.jezoensis,the trend of tissues nutrient concentration in B.ermanii with elevation is simpler,which suggest that the physiology of tissue nutrient of B.ermanii is less affected by elevation than P.jezoensis.(3)Different tree species have different needs for soil nutrients.The physiological changes of all tissues in B.ermanii were only correlated with total phosphorus,while the nutrient concentrations of all tissues in P.jezoensis were correlated with total nitrogen,total phosphate and total potassium,which indicated that B.ermanii was less affected by soil nutrients than P.jezoensis.Furthermore,one-year-old leaves N/P of P.jezoensis was less than 14,while one-year-old leaves N/P of B.ermanii more than 20 and had an increasing trend with elevation.Which suggested that B.ermanii growth may be more affected by phosphorus supply,and P.jezoensis growth may be more affected by nitrogen supply.P.jezoensis may be more sensitive to nitrogen deposition than B.ermanii in mountain environments.In conclusion,we found that compared with P.jezoensis,B.ermanii has a stronger NSC storage capability and adaptability to the hash mountainous environments,which may be a reason that it distributes in higher altitudes.Under the mountainous environments,B.ermanii responds more strongly to climate warming than P.jezoensis,while P.jezoensis responds more strongly to nitrogen deposition.Future studies on the treeline and its spatial formation and shift should to taking into account the physiological differences of tree species.