Nutrient Use Efficiency of Three Fast Growing Hardwood Species across a Resource Gradient

Attitudes regarding traditional energy sources have shifted toward renewable resources. Specifically, short-rotation woody crop supply systems have become more prevalent for biomass and biofuel production. However, a number of factors such as environmental and inherent resource availability can limit tree production. Given the intensified demand for wood biomass production, forest and plantation management practices are focusing on increasing productivity. Fertilizer application, while generally one of the least expensive silvicultural tools, can become costly if application rates exceed nutrient uptake or demand of the trees especially if it does not result in additional biomass production. We investigated the effect of water and varying levels of nitrogen application (56, 112, and 224 kg&#183N&#183ha&#451&#183yr&#451) on nutrient content, resorption efficiency and proficiency, N:P and the relationship with ANPP, as well as leaf- and canopy-level nutrient use efficiency of nitrogen, phosphorus, and potassium for Populus deltoides, Quercus pagoda, and Platanus occidentalis. P. deltoides and P. occidentalis reached their maximum nitrogen budget with the application of water suggesting old agricultural fields may have sufficient nutrient levels to sustain short-rotation woody crops negating the application of additional nitrogen for these two species. Additionally, for P. deltoides and Q. pagoda application of nitrogen appeared to increase the uptake of phosphorus however, resorption efficiency for these two species were more similar to studies conducted on nutrient poor sites. Nutrient resorption proficiency for all three nutrients and all three species were at levels below the highest rates of nitrogen application. These findings suggest maximum biomass production may not necessarily be tied to maximum nutrient application.

Responses of water productivity to irrigation and N supply for hybrid maize seed production in an arid region of Northwest China

Water and nitrogen（N） are generally two of the most important factors in determining the crop productivity. Proper water and N managements are prerequisites for agriculture sustainable development in arid areas. Field experiments were conducted to study the responses of water productivity for crop yield（WP_（Y-ET）） and final biomass（WP_（B-ET）） of film-mulched hybrid maize seed production to different irrigation and N treatments in the Hexi Corridor, Northwest China during April to September in 2013 and also during April to September in 2014. Three irrigation levels（70%–65%, 60%–55%, and 50%–45% of the field capacity） combined with three N rates（500, 400, and 300 kg N/hm^2） were tested in 2013. The N treatments were adjusted to 500, 300, and 100 kg N/hm^2 in 2014. Results showed that the responses of WP_（Y-ET） and WP_（B-ET） to different irrigation amounts were different. WP_（Y-ET） was significantly reduced by lowering irrigation amounts while WP_（B-ET） stayed relatively insensitive to irrigation amounts. However, WP_（Y-ET） and WP_（B-ET） behaved consistently when subjected to different N treatments. There was a slight effect of reducing N input from 500 to 300 kg/hm^2 on the WP_（Y-ET） and WP_（B-ET）, however, when reducing N input to 100 kg/hm^2, the values of WP_（Y-ET） and WP_（B-ET） were significantly reduced. Water is the primary factor and N is the secondary factor in determining both yield（Y） and final biomass（B）. Partial factor productivity from applied N（PFP_N） was the maximum under the higher irrigation level and in lower N rate（100–300 kg N/hm^2） in both years（2013 and 2014）. Lowering the irrigation amount significantly reduced evapotranspiration（ET）, but ET did not vary with different N rates（100–500 kg N/hm^2）. Both Y and B had robust linear relationships with ET, but the correlation between B and ET（R^2=0.8588） was much better than that between Y and ET（R^2=0.6062）. When ET increased, WP_（Y-ET） linearly increased and WP_（B-ET） decreased. Taking the indices of Y, B, WP_（Y-ET）, WP_（B-ET） and PFP_N into account, a higher irrigation level（70%–65% of the field capacity） and a lower N rate（100–300 kg N/hm^2） are recommended to be a proper irrigation and N application strategy for plastic film-mulched hybrid maize seed production in arid Northwest China.

Biomass, productivity and energy use efficiency of climax vegetation on Dinghu Mountains, Guangdong, China

The biomass, primary productivity and energy use efficiency of photosysthetically active radiation of climax vegetation on Dinghu Mountains, in low subtropical were studied with the tree-harvested, litter gather, CO, analysis methods, etc. The results show that the leaf area index of the community is 17; biomass, 363 t·（hm2） -1 · a-1, total productivity, 132 t· （hm2） -1 · a-1; primary productivity, 23.2 t · （hm2） -1· a-1; litter-fall, 9.2t ·（hm2）-1·a-1; death tree, 3.9 t·（hm2）-1· a-1, animal-eating, 0.6 t·（hm2） -1 · a-1; net productivity, 9.5 t·（hm2）-1· a-1.

Photosynthetic performance of switchgrass and its relation to field productivity：A three-year experimental appraisal in semiarid Loess Plateau

To reveal photosynthetic characteristics and biomass yield is important for evaluating introduced species adaptation to local environments. A field experiment was conducted over three consecutive years（2011–2013） to evaluate photosynthetic characteristics, soil water content, aboveground biomass accumulation, and water use efficiency（WUE） in switchgrass（Panicum virgatum L.） populations exposed to three row spacing（20, 40 and 60 cm） treatments in two growth months（June and August） on the semiarid Loess Plateau of China. Results indicated that net photosynthetic rate（Pn）, transpiration rate（Tr）, instantaneous water use efficiency（WUEi） and plant height of switchgrass showed an increased trend, but aboveground biomass production and WUE showed an decreased trend with enlarged row spacings over the three years. The maximum daily mean Pn values（17.9, 18.4 and 19.7 μmol CO2 m^（-2） s^（-1）） were observed in 2011, and the highest aboveground biomass production（67 771.8, 6 976.8 and 6 609.2 kg ha^（-1）） were recorded in 2012 for 20, 40 and 60 cm, respectively. A close correlation between tiller numbers and aboveground biomass production（r=0.907） was observed. Pn was positively and significantly correlated with biomass per tiller, but it showed a negative correlation with aboveground biomass production. Our results confirm that wide row spacing is beneficial for single plant development, while narrow row spacing favors biomass production and water use of switchgrass in the region. It also implies that single leaf growth and performance could explain the switchgrass community density differences, while fails to account for the aboveground biomass production.

Responses of Amygdalus pedunculata Pall.in the sandy and loamy soils to water stress

Amygdalus pedunculata Pall.is a major species that is widely planted in afforested soils with different textures in the transitional zone between Mu Us Desert and Loess Plateau,China.However,the responses of A.pedunculata to increasing intensity of water stress in different textural soils are not clear.Here,we conducted a soil column experiment to evaluate the effects of different textures(sandy and loamy)on water consumption,water use efficiency(WUE),biomass accumulation and ecological adaptability of A.pedunculata under increasing water stress,i.e.,90%(±5%)FC(field capacity),75%(±5%)FC,60%(±5%)FC,45%(±5%)FC and 30%(±5%)FC in 2018.A.pedunculata grown in the sandy soil with the lowest(30%FC)and highest(90%FC)water contents had respectively 21.3%-37.0%and 4.4%-20.4%less transpiration than those with other water treatments(45%-75%FC).In contrast,A.pedunculata transpiration in the loamy soil decreased with decreasing water content.The magnitude of decrease in transpiration increased with increasing level of water deficit(45%and 30%FC).Mean daily and cumulative transpirations of the plant were significantly lower in the sandy soil than in the loamy soil under good water condition(90%FC),but the reverse was noted under water deficit treatments(45%and 30%FC).Plant height,stem diameter and total biomass initially increased with decreasing water content from 90%to 75%FC and then declined under severe water deficit conditions(45%and 30%FC)in the sandy soil.However,these plant parameters decreased with decreasing water content in the loamy soil.WUE in the sandy soil was 7.8%-12.3%higher than that in the loamy soil,which initially increased with decreasing water content from 90%to 75%FC and then declined under water deficit conditions(45%and 30%FC).The study showed that plant transpiration,biomass production and WUE responded differentially to increasing intensity of water stress in the sandy and loamy soils.The contrasting responses of A.pedunculata to water stress in different textural soils can guide future revegetation programs in the northern region of Chinese Loess Plateau by considering plant adaptability to varying soil and water conditions.

A global meta-analysis of woody plant responses to elevated CO_(2):implications on biomass,growth,leaf N content,photosynthesis and water relations

Background:Atmospheric CO_(2)may double by the year 2100,thereby altering plant growth,photosynthesis,leaf nutrient contents and water relations.Specifically,atmospheric CO_(2)is currently 50%higher than pre-industrial levels and is projected to rise as high as 936μmol mol^(−1)under worst-case scenario in 2100.The objective of the study was to investigate the effects of elevated CO_(2)on woody plant growth,production,photosynthetic characteristics,leaf N and water relations.Methods:A meta-analysis of 611 observations from 100 peer-reviewed articles published from 1985 to 2021 was conducted.We selected articles in which elevated CO_(2)and ambient CO_(2)range from 600–1000 and 300–400μmol mol^(−1),respectively.Elevated CO_(2)was categorized into<700,700 and>700μmol mol^(−1)concentrations.Results:Total biomass increased similarly across the three elevated CO_(2)concentrations,with leguminous trees(LTs)investing more biomass to shoot,whereas non-leguminous trees(NLTs)invested to root production.Leaf area index,shoot height,and light-saturated photosynthesis(A_(max))were unresponsive at<700μmol mol^(−1),but increased significantly at 700 and>700μmol mol^(−1).However,shoot biomass and A_(max)acclimatized as the duration of woody plants exposure to elevated CO_(2)increased.Maximum rate of photosynthetic Rubisco carboxylation(V_(cmax))and apparent maximum rate of photosynthetic electron transport(J_(max))were downregulated.Elevated CO_(2)reduced stomatal conductance(g_(s))by 32%on average and increased water use efficiency by 34,43 and 63%for<700,700 and>700μmol mol^(−1),respectively.Leaf N content decreased two times more in NLTs than LTs growing at elevated CO_(2)than ambient CO_(2).Conclusions:Our results suggest that woody plants will benefit from elevated CO_(2)through increased photosyn-thetic rate,productivity and improved water status,but the responses will vary by woody plant traits and length of exposure to elevated CO_(2).