Study on the Soil Moisture Stress Level in Regulated Deficit Irrigation Experiment

On the basis of discussing the influencing mode of plant moisture stress on plant physiological process and the division of soil moisture availability range, the water suction values partitioning soil moisture were put forward, and then the corresponding water moistures under water stress were obtained by conversing together with characteristic curve of water moisture.

Adaptive responses of Acer ginnala, Pyrus ussuriensis and Prunus davidiana seedlings to soil moisture stress

One-year-old seedlings of Amur maple (Acer ginnala Maxim), Ussurian pear (Pyrus ussuriensis Maxim) and David peach (Prunus davidiana Carr) were planted in pots in greenhouse and treated with four different soil moisture contents (75.0%, 61.1%, 46.4% and 35.4%). The results showed that net photosynthesis rate (NPR), transpiration rate (TR) and stomatal conductance (Sc) of seedlings of the three species decreased with the decease of soil moisture content, and Amur maple seedlings had the greatest change in those physiological indices, followed by Ussurian pear, David peach. Amur maple and Ussurian pear seedlings also presented a decrease tendency in water use efficiency (WUE) under lower soil moisture content, whereas this was reversed for David peach. Under water stress the biomass allocation to seedling root had a significant increase for all the experimental species. As to root/shoot ratio, Amur maple seedlings had the biggest increase, while David peach had the smallest increase. The leaf plasticity of Amur maple seedlings was greater, the leaf size and total leaf area decreased significantly as the stress was intensified. No significant change of leaf size and total leaf area was found in seedlings of Ussurian pear and David peach. It was concluded that Amur maple was more tolerant to soil moisture stress in comparison with David peach and Ussurian pear.

Larch growth across thermal and moisture gradients in the Siberian Mountains

Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-sensitive Siberian pine(Pinus sibirica Du Tour)responded differently to climate change along the elevational thermal and precipitation gradients.We studied the influence of air temperature,precipitation,soil moisture,and atmospheric drought(indicated by the drought index SPEI)on larch and pine growth along the southward megaslope of the West Sayan Ridge.We found that since 2000 climate change resulted in increasing larch and pine radial growth index(GI)(c.1.5–3times)within treeline(2000–2300 m)and timberline(1900–2000 m)ecotones,i.e.within high precipitation zones.Within the forest-steppe ecotone(1100–1200 m)in which L.sibirica is the only species,larch GI stagnated or even decreased.The total forested area increased since 2000 up to+50%in the high elevations,whereas in the low elevations(<1400 m)area changes were negligible.Within treeline and timberline,trees’GI was stimulated by summer temperature.Meanwhile,temperature increase in early spring reduces GI due to living tissue activation followed by tissue damage by desiccation.Within forest-steppe,larch radial growth was mostly dependent on soil moisture.Warming shifted dependence on moisture to the early dates of the growing period.Acute droughts decreased GI within forest-steppe as well as within treeline,whereas the drought influence on both species within highlands was insignificant.Within forest-steppe seedlings establishment was poor,whereas it was successful within treeline and timberline.Current climate change leads to stagnation or even decrease in Larix sibirica growth in the southern lowland habitat.In combination with poor seedlings establishment,reduced growth threatens the transformation of open lowland forests into forest-steppe and steppe communities.Meanwhile,in the highlands warming facilitated the growth of Siberian larch and pine and the increase of forested area.

Experimental and theoretical study on thermal and moisture characteristics of new-type bamboo structure wall

Thermal and moisture characteristics of the bamboo structure wall were tested in natural climate and three representative variation processes of heat and moisture： heating from solar radiation in summer at normal temperature and humidity, heating from solar radiation in summer at normal temperature and high humidity after rain, humidifying from brash in summer at high temperature and normal humidity. The results show that, in summer, the largest temperature difference between external and internal surface of the 28 mm-thick bamboo plywood wall is 11.73℃ （at 15：40） and the largest strain difference is 136 μm/m （at 18：50）, both in ambient and indoor conditioned environment. In heating process, lengthways of the wall surface are in contracting strain while transverse ways are in expanding strain at initial stage and in contracting strain during later period. When the high temperature wall is humidified by rain, the surface temperature drops, moisture content increases and the expanding strain is presented on the surface during the whole process. Temperature and moisture content are two important factors which affect thermal and moisture stress （TMS） of the bamboo structure wall. The TMS is not only related to temperature and moisture content, but also greatly affected by temperature gradient, moisture content gradient and rates of changing.

Tree clusters migration into alpine tundra,Siberia

We hypothesize that in mountain windy habitat trees formed clusters(hedges)as adaptive structures for seedlings’rooting,survival,and tress’upslope migration.We studied hedges formed by Siberian pine(Pinus sibirica du Tour)and larch(Larix sibirica Ledeb.)within the treeline ecotone in southern Siberian Mountains,investigated hedges formation,evolution,habitat amelioration,and analyzed tree’s growth index(GI)dependence on the eco-climate variables(air temperature,precipitation,soil moisture,wind speed)and relief features(elevation,aspect,slope steepness,and terrain curvature).We conducted a ground survey,measured biometrical parameters of trees and hedges,determined species composition and tree physiognomy,soil types and nutrient contents,and sampled wood cores and applied dendrochronology for trees’GI analysis.With high-resolution satellite scenes for hedge detection and upslope migration,we found that winter winds and soil moisture are the main constraints of trees’settlement and growth.Hedge formation always links with wind-sheltered microtopography features(boulders,local depressions or felled trees).Once the first tree is established,a positive feedback is aroused that facilitates seedling rooting and in-hedge habitat amelioration.Trees form a streamlined dense“common crown”that mitigates adverse winter wind influence.Hedges always orient along the prevailing winds,and trees’uphill migration occurs by seedlings establishment within the leeward hedge side.Hedge growth facilitates soil formation and fertilization.The concentration of nutrients(K,P,N and S)within hedges exceeds the background by 1.5-5.5 times.Hedge extension leads to increased snow accumulation that mitigates the influence of desiccation and snow abrasion and mitigates seasonal water stress.In the extremely harsh windy habitat,inhedge trees present in mat,prostrate or krummholz forms.With warming,tree stems and even twigs turn upright.Notably that GI dependence on the wind speed is insignificant until prostrated trees get turning upright.Since that,the negative correlation between GI and wind speed is arisen with subsequent decrease since hedges form streamlined crown.Hedge growth also leads to a“phytofield”formation(i.e.,grasses,lichen,moss and small bushes growth)around the hedges that,in its turn,encourages seedling rooting which is about triple more efficient than outside the phytofield.Larch,in comparison with Siberian pine,is less often formed hedges.GI of both species is stimulated by warmer air temperature in the beginning of the growth season.Meanwhile,larch GI has stronger response to elevated temperatures and less dependent on soil moisture.This indicates larch is a potential substitute of Siberian pine in a warmer and dryer climate.Hedges in warming climate evolve into closed stands due to both in-hedge tree growth and filling gaps between hedges by different tree species.

The effect of biochar on mycorrhizal fungi mediated nutrient uptake by coconut(Cocos nucifera L.)seedlings grown on a Sandy Regosol

Biochar amendment of soil may ameliorate inherently infertile soils,such as in the typical coconut(Cocos nucifera L.)growth areas along tropical coasts,where,moreover,temporary moisture stress commonly occurs.We conducted a pot experiment to evaluate the effects of biochar soil amendment(1%w/w)produced from Gliricidia sepium stems(BC-Gly)and rice husks(BC-RiH)on the growth of coconut seedlings and on N and P uptake mediated by mycorrhizae under wet or dry conditions in a Sandy Regosol.The pots were divided into root and hyphal zones by a nylon mesh,where 15N labelled N and P nutrients were only provided in the hyphal zone.Under wet conditions,biochar applica-tion did not affect plant growth,while under dry conditions,the BC-Gly increased root and plant growth similar to that under wet conditions.BC-Gly increased the acidic pH of the soil to a neutral level,and the microbial community shifted towards a higher fungal abundance.The P accumulated(Pacc)in roots was higher with BC-Gly and BC-RiH under dry and wet conditions,respectively.Pacc weakly correlated with the abundance of arbuscular mycorrhizal fungi(AMF)in the hyphal zone.With BC-Gly roots showed lower N derived from fertilizer.We conclude that biochar application has no impact on crop growth under wet conditions,while under dry conditions,BC-Gly stimulates crop growth and P uptake,probably through liming induced P availability but also possibly by some enhancement of AMF growth.The shift in the fungal-oriented microbial community and reduced plant fertilizer N uptake suggested that BC-Gly acted as an additional N source.