Time-domain reflectometry (TDR) is increasingly used for field soil water estimation because the measurement is nondestructive and less affected by soil texture, bulk density and temperature. However, with the increase in instrument resolution, the influences of soil bulk density and temperature on TDR soil moisture measurements have been reported. The influence is primarily caused by changes in soil and water dielectric permittivity when soil compaction and temperature varies. The objective of this study is to quantify the influence of soil bulk density and temperature, and to provide the corresponding correction methods. Data collected from sand, sandy loam, loam and clay loam show a linear relationship between the square root of dielectric constant of dry soil and bulk density, and a bulk density correction formula has been developed. The dielectric permittivity of soil solids estimated using this formula is close to that of oxides of aluminium, silicon, magnesium and calcium. Data collection from sandy loam show a noticeable decrease in measured soil moisture with increase in temperature when the volumetric soil water content is above 0Ð30 m 3 m 3 . A temperature-correction equation has been developed, which could provide the corrected soil moisture based on soil temperature and TDR-measured moisture. The effect of clay content has been detected, but it is not statistically significant. High clay contents cause the underestimation of soil water content in the low moisture range and overestimation of soil water content in the high moisture range.

Chilling stress affects plant growth and productivity. However, the multi-underlying mechanisms of chilling tolerance are not well understood. Arabidopsis PCaP2 is involved in regulating the dynamic of microtubules (MTs) and F-actin and Ca2+-binding ability. Here, the results showed that the PCaP2 expression was highly induced in roots, cotyledons, true leaves, lateral roots and flowers under cold stress. Compared with the wild type, PCaP2-overexpressing plants displayed the enhanced tolerance, whereas its RNAi and mutant were more sensitive in seed germination, seedling and reproductive growth under chilling stress in Arabidopsis. In addition, PCaP2 was also a positive regulator of ABA signaling pathway by analyzing the expression of PCaP2 and the phenotypes of PCaP2-overexpressing, mutant and RNAi plants under ABA treatment. Interestingly, disruption of PCaP2 inhibited the expression of CBF1, -3 and CBF-target COR genes, while increased the CBF2 expression in response to cold or ABA. Moreover, we found that SnRK2s were involved in cold stress and PCaP2 mutants down-regulated the transcription level of SnRK2.2, -2.3 and SnRK2-mediated downstream genes including ABF2, RD29A, KIN1, KIN2, but up-regulated SnRK2.6, ABF1, -3, -4 in ABA and cold treatments. It is well-accepted that PCaP2 as a Ca2+-binding protein triggers the gene expression to enhance plant chilling tolerance. Our further studies showed that MT destabilizing activity of PCaP2, but not F-actin-severing function, may be involved in chilling stress. Taken together, our results highlight that PCaP2 plays an important role in chilling tolerance and ABA response by triggering the CBF- and SnRK2-meditated transcriptional regulatory pathways, providing novel evidences of underlying mechanisms of multi-pathways in chilling stress.

Water stress has a major influence on plant growth, development, and productivity. However, the cross-talk networks involved in drought tolerance are not well understood. Arabidopsis PCaP2 is a plasma membrane-associated Ca2+-binding protein. In this study, we employ qRT-PCR and β-glucuronidase (GUS) histochemical staining to demonstrate that PCaP2 expression was strongly induced in roots, cotyledons, true leaves, lateral roots, and whole plants under water deficit conditions. Compared with the wild type (WT) plants, PCaP2-overexpressing (PCaP2-OE) plants displayed enhanced water deficit tolerance in terms of seed germination, seedling growth, and plant survival status. On the contrary, PCaP2 mutation and reduction via PCaP2-RNAi rendered plants more sensitive to water deficit. Furthermore, PCaP2-RNAi and pcap2 seedlings showed shorter root hairs and lower relative water content compared to WT under normal conditions and these phenotypes were exacerbated under water deficit. Additionally, the expression of PCaP2 was strongly induced by exogenous abscisic acid (ABA) and salicylic acid (SA) treatments. PCaP2-OE plants showed insensitive to exogenous ABA and SA treatments, in contrast to the susceptible phenotypes of pcap2 and PCaP2-RNAi. It is well-known that SNF1-related kinase 2s (SnRK2s) and pathogenesis-related (PRs) are major factors that influence plant drought tolerance by ABA- and SA-mediated pathways, respectively. Interestingly, PCaP2 positively regulated the expression of drought-inducible genes (RD29A, KIN1, and KIN2), ABA-mediated drought responsive genes (SnRK2.2, -2.3, -2.6, ABF1, -2, -3, -4), and SA-mediated drought responsive genes (PR1, -2, -5) under water deficit, ABA, or SA treatments. Taken together, our results showed that PCaP2 plays an important and positive role in Arabidopsis water deficit tolerance by involving in response to both ABA and SA signals and regulating root hair growth. This study provides novel insights into the underlying cross-talk mechanisms of plants in response to water deficit stress.

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