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1.
Sci Total Environ ; 904: 166945, 2023 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-37699482

RESUMO

The increasing frequency of drought and decline in groundwater levels are causing ecophysiological changes in woody plants, particularly in desert ecosystems in arid regions. However, the combined effects of meteorological and hydrological droughts on perennial desert plants, especially phreatophytes, remain poorly understood. To address this knowledge gap, we conducted a 5-year precipitation exclusion experiment at two sites with contrasting groundwater depths in the Gurbantunggut Desert located in northwest China. Our study aimed to investigate the impacts of precipitation exclusion and groundwater depth decline on multiple traits of H. ammodendron. We found that long-term precipitation exclusion enhanced midday leaf water potential, stomatal conductance, chlorophyll content, root nonstructural carbohydrates concentration, leaf starch concentration, but decreased water use efficiency. Groundwater drawdown decreased predawn and midday leaf water potentials, maximum net photosynthetic rate, stomatal conductance, Huber value, stem water δ18O, but enhanced water use efficiency and branch nonstructural carbohydrates concentration. A combination of precipitation exclusion and groundwater depth decline reduced Huber value, but did not show exacerbated effects. The findings demonstrate that hydrological drought induced by groundwater depth decline poses a greater threat to the survival of H. ammodendron than future changes in precipitation.


Assuntos
Chenopodiaceae , Água Subterrânea , Ecossistema , Secas , Água/análise , Folhas de Planta/química , Plantas , Carboidratos
2.
Sci Total Environ ; 854: 158802, 2023 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-36115397

RESUMO

In recent year, widespread declines of Populus bolleana Lauche trees (P. bolleana, which dieback from the top down) and Haloxylon ammodendron shrubs (H. ammodendron, which dieback starting from their outer canopy) have occurred. To investigate how both intra-canopy hydraulic changes and plasticity in hydraulic properties create differences in vulnerability between these two species, we conducted a drought simulation field experiment. We analyzed branch hydraulic vulnerability, leaf water potential (Ψ), photosynthesis (A), stomatal conductance (gs), non-structural carbohydrate (NSCs) contents and morphological traits of the plants as the plants underwent a partial canopy dieback. Our results showed that: (1) the hydraulic architecture was very different between the two life forms; (2) H. ammodendron exhibited a drought tolerance response with weak stomatal control, and thus a sharp decline in Ψ while P. bolleana showed a drought avoidance response with tighter stomatal control that maintained a relatively stable Ψ; (3) the Ψ of H. ammodendron showed relative consistent symptoms of drought stress with increasing plant stature, but the Ψ of P. bolleana showed greater drought stress in higher portions of the crown; (4) prolonged drought caused P. bolleana to consume and H. ammodendron to accumulate NSCs in the branches of their upper canopy. Thus, the prolonged drought caused the shoots of the upper canopy of P. bolleana to experience greater vulnerability leading to dieback of the upper branches first, while all the twigs of the outer canopy of H. ammodendron experienced nearly identical degrees of vulnerability, and thus dieback occurred uniformly. Our results indicate that intra-canopy hydraulic change and their plasticity under drought was the main cause of the observed canopy dieback patterns in both species. However, more work is needed to further establish that hydraulic limitation as a function of plant stature was the sole mechanism for causing the divergent canopy dieback patterns.


Assuntos
Secas , Árvores , Árvores/fisiologia , Folhas de Planta/fisiologia , Água/fisiologia , Madeira , Carboidratos
3.
Ying Yong Sheng Tai Xue Bao ; 33(3): 733-741, 2022 Mar.
Artigo em Chinês | MEDLINE | ID: mdl-35524526

RESUMO

Groundwater is an important water source for phreatophytic shrubs in arid desert areas. In order to understand the impacts of groundwater depth on functional traits of phreatophytic shrubs, two groups of groundwater levels (2 and 3.5 m) were set up using lysimeter with automatic water replenishing instrument. We measured hydraulic traits, gas exchange characteristics, and root morphological parameters of young Haloxylon ammodendron during the growing season. The results showed that predawn assimilating branch water potential, osmotic potential at full turgor, and root length ratio of young H. ammodendron in the groundwater depth of 3.5 m were lower by 48.2%, 41.5% and 56.7% than that under groundwater depth of 2 m, respectively, while maximum net photosynthetic rate of late growing season, root volume, specific root length and specific root area of fine root were 75.7%, 41.0%, 273.7% and 67.7% higher, respectively. Midday water potential and water content of assimilating branch tended to decrease first in the early growing season and then increase in the late growing season. Root distribution of young H. ammodendron along soil profile showed a significant positive correlation between the average root diameter and soil depth, while the proportion of fine root surface area showed a significant negative correlation with soil depth at both groundwater levels. There was synergy of aboveground assimilating branch hydraulic traits and photosynthetic capacity with belowground root morphological traits in young H. ammodendron. Under the condition of increasing groundwater depth, young H. ammodendron adopted the ecological strategies of reducing predawn assimilating branch water potential and osmotic potential at full turgor, and increasing root diameter and length to enhance water deficit tolerance and expanding the area of water uptake to sustain their survival.


Assuntos
Chenopodiaceae , Fabaceae , Água Subterrânea , Fotossíntese , Solo , Água/análise
4.
Inorg Chem ; 38(22): 4993-4999, 1999 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-11671242

RESUMO

The reactions of Me(2)SiCl(2), Ph(2)SiCl(2), and Ph(2)GeCl(2) with LiP(H)B(N(i)Pr(2))(2) in a 1:2 ratio and the reaction of Ph(2)SiCl(2) with LiP(H)B(N(i)Pr(2))[N(SiMe(3))(2)] in a 1:2 ratio give good yields of the respective diphosphinosilanes, Me(2)Si[P(H)B(N(i)Pr(2))(2)](2), Ph(2)Si[P(H)B(N(i)Pr(2))(2)](2), Ph(2)Ge[P(H)B(N(i)Pr(2))(2)](2), and Ph(2)Si[P(H)B(N(i)Pr(2))[N(SiMe(3))(2)]](2). These species, when combined with BuLi in a 1:2 ratio, give lithium diphosphinosilanes and -germanes of the general type (DME.Li)(2){[PB(NR(2))(2)](2)ER'(2)}. All of the species have been characterized by spectroscopic methods. The molecular structures of three of the lithio compounds, (DME.Li)(2){[PB(N(i)Pr(2))(2)](2)SiPh(2)} (11), (DME.Li)(2){[PB(N(i)Pr(2))N(SiMe(3))(2)](2)SiPh(2)} (15), and (DME.Li)(2){[PB(N(i)Pr(2))(2)](2)GePh(2)} (13), have been determined by X-ray diffraction techniques. 11 crystallized in the triclinic space group P&onemacr; with a = 11.071(2) Å, b = 14.937(3) Å, c = 18.080(4) Å, alpha = 91.31(3) degrees, beta = 101.23(3) degrees, gamma = 109.95(3) degrees, and Z = 2, and 13 crystallized in the triclinic space group P&onemacr; with a = 11.083(1) Å, b = 14.978(2) Å, c = 18.134(2) Å, alpha = 91.17(1) degrees, beta = 101.43(1) degrees, gamma = 110.05(1) degrees, and Z = 2. 15 crystallized in the monoclinic space group P2(1)/n with a = 11.939(2) Å, b = 24.516(3) Å, c = 21.572(3) Å, beta = 101.52(1) degrees, and Z = 4. The reactions of the lithio compounds were surveyed with R(2)ECl(2) reagents. The metathesis reactions are sluggish, but the 1:1 reaction of (DME.Li)(2){[PB(N(i)Pr(2))(2)](2)GePh(2)} with (t)Bu(2)SnCl(2) gave the four-membered-ring compound The 1:2 reaction of Me(2)(Cl)SiSi(Cl)Me(2) with LiP(H)B(N(i)Pr(2))(2) yielded the (borylphosphino)silane [Me(2)SiP(H)B(N(i)Pr(2))(2)](2).

5.
Inorg Chem ; 37(3): 490-495, 1998 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-11670299

RESUMO

The 1:1 reactions with (R(3)P)(2)MCl(2) (M = Ni, Pd, and Pt) have been surveyed, and bicyclic cage compounds containing boron, phosphorus and transition metal (Ni, Pd, or Pt) atoms have been isolated and characterized. The molecular structures of the species (Et(3)P)(2)Pd(PBN(i)Pr(2))(2) (2), (Et(3)P)(2)Pd(PBtmp)(2) (3), and (Et(3)P)(2)Pt(PBN(i)Pr(2))(2) (4) have been determined by single-crystal X-ray diffraction techniques. 2 crystallized in the monoclinic space group C2/c with a = 20.212(4) Å, b = 10.225(1) Å, c = 17.460(2) Å, beta = 107.72(1) degrees, and Z = 4. 3 crystallized in the orthorhombic space group P2(1)2(1)2(1) with a = 12.606(1) Å, b = 12.618(1) Å, c = 24.221(3) Å, and Z = 4. 4 crystallized in the monoclinic space group C2/c with a = 20.195(3) Å, b = 10.187(2) Å, c = 17.280(2) Å, beta = 107.53(7) degrees, and Z = 4. The spectroscopic and structural features of the new cage compounds are discussed in relation to their main group element cage analogs.

6.
7.
Inorg Chem ; 36(6): 1070-1075, 1997 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-11669670

RESUMO

The 1:1 reactions of [((i)()Pr(2)N)BP(H)B(N(i)()Pr(2))PLi.DME] (1) and [(tmp)BP(H)B(tmp)PLi.DME] (2; tmp = 2,2,6,6-tetramethylpiperidino) with organylhalostannanes have been examined, and stannyl-substituted diphosphadiboretanes, (R(2)N)BP(H)B(NR(2))PSn(Cl)R'(2) (R(2)N = (i)()Pr(2)N, tmp; R' = Me, (t)()Bu) have been isolated and characterized. Dehydrohalogenation of these compounds with (t)()BuLi produced bicyclic cage compounds P(2)(R(2)NB)(2)SnR'(2) (R(2)N = (i)()Pr(2)N (9), tmp (8); R' = (t)()Bu) or an oligomer [-P(R(2)NB)(2)PSn(R'(2))-] (R(2)N = tmp; R' = Me). The 2:1 reactions of R'(2)SnCl(2) with 1 and 2 have been studied, and with a small R' group (Me) a disubstitution product, [HP(tmpB)(2)P](2)SnMe(2) (11), is obtained. With a larger R' group ((t)()Bu), cage products P(2)(tmpB)(2)Sn(t)()Bu(2) and P(2)((i)()Pr(2)NB)(2)Sn(t)()Bu(2) are isolated. The molecular structures of 8 and 9 have been determined by single crystal X-ray diffraction techniques, and these structures and their spectroscopic features are discussed in relation to other boron-phosphorus cage compounds.

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