Effects of vegetation, terrain and soil layer depth on eight soil chemical properties and soil fertility based on hybrid methods at urban forest scale in a typical loess hilly region of China.

Although the spatial mapping and fertility assessment of soil chemical properties (SCPs) are well studied in the Loess Plateau region of China at farmland scale, little is known about spatial mapping the SCPs and their fertility and their influence factors at urban forest scale. The objectives of this study were to (1) compare the performance of two spatial interpolation methods, Ordinary kriging (OK) and regression kriging (RK), and (2) explain the relationships of the vegetation, terrain, and soil layer depth between the eight SCPs and their fertility, and (3) find the limiting factors of soil comprehensive fertility in this study area? The Yan'an urban forest was taken as study case, used hybrid spatial interpolation methods based on OK and RK to mapping eight SCPs and the soil fertility in each soil layer (0-20 cm, 20-40 cm, and 40-60 cm) for 285 soil samples. The results indicated that RK outperformed OK for total nitrogen (TN), available potassium (AK), organic matter (OM) in 0-60 cm profile and available phosphorus (AP) in the 0-20 cm and 40-60 cm soil layers because RK considered the impact of terrain. The terrain factors, comprising the relative terrain position, slope, aspect, and relative elevation significantly affected the SCPs and spatial heterogeneity of fertility, where the vegetation cover types determined the average SCPs to some extent. On average, the six SCPs (except total potassium and AP) and the fertility decreased as the soil layer depth increased. Ten vegetation cover types comprising broadleaved mixed natural forest (BM), cultivated land (CL), economic forest (EF), grassland (GL), Platycladus orientalis natural forest (PON), Platycladus orientalis plantation (POP), Pinus tabuliformis plantation (PT), Quercus wutaishanica natural forest (QW), Robinia pseudoacacia plantation (RP), and Shrubwood (SW) were associated with significant differences in TN, OM, AN, AP, and AK, across the three soil layers. QW, PON, and BM also had higher content of TN, OM, AN, and AK contents than the other vegetation cover types. There were small differences in TK, AK, and pH among the 10 vegetation cover types. We concluded that AN, TN, and OM are the limiting factors of soil comprehensive fertility in this region. These results improve understanding of the spatial mapping, influence and limiting factors of SCPs and their fertility at urban forest scales.

Experimental evidence for negative turgor pressure in small leaf cells of Robinia pseudoacacia L versus large cells of Metasequoia glyptostroboides Hu et W.C.Cheng. 1. Evidence from pressure-volume curve analysis of dead tissue.

This paper provides a mini-review of evidence for negative turgor pressure in leaf cells starting with experimental evidence in the late 1950s and ending with biomechanical models published in 2014. In the present study, biomechanical models were used to predict how negative turgor pressure might be manifested in dead tissue, and experiments were conducted to test the predictions. The main findings were as follows: (i) Tissues killed by heating to 60 or 80 °C or by freezing in liquid nitrogen all became equally leaky to cell sap solutes and all seemed to pass freely through the cell walls. (ii) Once cell sap solutes could freely pass the cell walls, the shape of pressure-volume curves was dramatically altered between living and dead cells. (iii) Pressure-volume curves of dead tissue seem to measure negative turgor defined as negative when inside minus outside pressure is negative. (iv) Robinia pseudoacacia leaves with small palisade cells had more negative turgor than Metasequoia glyptostroboides with large cells. (v) The absolute difference in negative turgor between R. pseudoacacia and M. glyptostroboides approached as much as 1.0 MPa in some cases. The differences in the manifestation of negative turgor in living versus dead tissue are discussed.

Experimental evidence for negative turgor pressure in small leaf cells of Robinia pseudoacacia L versus large cells of Metasequoia glyptostroboides Hu et W.C. Cheng. 2. Höfler diagrams below the volume of zero turgor and the theoretical implication for pressure-volume curves of living cells.

The physiological advantages of negative turgor pressure, Pt , in leaf cells are water saving and homeostasis of reactants. This paper advances methods for detecting the occurrence of negative Pt in leaves. Biomechanical models of pressure-volume (PV) curves predict that negative Pt does not change the linearity of PV curve plots of inverse balance pressure, PB , versus relative water loss, but it does predict changes in either the y-intercept or the x-intercept of the plots depending on where cell collapse occurs in the PB domain because of negative Pt . PV curve analysis of Robinia leaves revealed a shift in the x-intercept (x-axis is relative water loss) of PV curves, caused by negative Pt of palisade cells. The low x-intercept of the PV curve was explained by the non-collapse of palisade cells in Robinia in the PB domain. Non-collapse means that Pt smoothly falls from positive to negative values with decreasing cell volume without a dramatic change in slope. The magnitude of negative turgor in non-collapsing living cells was as low as -1.3 MPa and the relative volume of the non-collapsing cell equaled 58% of the total leaf cell volume. This study adds to the growing evidence for negative Pt .

Significance of exine shedding in Cupressaceae-type pollen.

In conifers, which have non-saccate Cupressaceae-type pollen, the pollen must land on a pollination drop or be picked up by the pollination drop from the surface of the cone near the ovule before it can be taken into the ovule. After contact with the drop, the pollen intine absorbs moisture from the drop, expands and the exine is shed. In this study the significance of the shedding of the exine is interpreted from experiments in which simulated pollination drops and micropyles were used to determine the movement of pollen and other particles in suspension. The non-expanded pollen, which can be observed upon contact with the pollination drop, sheds the exine, which then functions as a non-elastic particle, while the pollen from which the exine was shed swells and functions as an elastic particle because it is enclosed by the flexible intine. Non-elastic particles are not easily transferred through narrow passages (the micropyle and micropylar canal) and tend to plug these passages. However, elastic particles, such as the swollen pollen, are easily transferred along narrow passages even when non-elastic particles are present. The simulated experiments demonstrate that exine shedding is an important feature in getting pollen through the narrow micropyle and micropylar canal to the nucellus of the ovule.

Effect of air temperature on forecasting the start of Cupressaceae pollen type in Ponferrada (Leon, Spain).

In order to survive periods of adverse cold climatic conditions, plant requirements are satisfied by means of physiological adaptations to prevent cells from freezing. Thus, the growth of woody plants in temperate regions slows down and they enter into a physiological state called dormancy. In order to identify the chilling and heat requirements to overcome the dormancy period of Cupressaceae pollen type in the south of Europe, we have carried out our study with aerobiological data from a 10-year (1996-2005) period in Ponferrada, León (Spain). For the chilling requirements the best result was with a threshold temperature of 7.1 degrees C and an average of 927 CH. Calculation of heat requirements was carried out with maximum temperature, with 490 growth degree days (GDD) needed, with a threshold temperature of 0 degrees C. We have used the 2002-2003, 2003-2004 and 2004-2005 periods in order to determine the real validity of the model. We have not used these years in developing the models. The dates predicted differ in only a few days from those observed: in 2002-2003 there was a difference of 11 days, in 2003-2004 predicted and observed dates were the same, but in 2004-2005 the difference obtained was of 43 days.

Study of male sterility in Taiwania cryptomerioides Hayata (Taxodiaceae).

A study of male sterility over a period of three consecutive years on a conifer species endemic to Taiwan, Taiwania cryptomerioides Hayata (Taxodiaceae), was done for this article. With the aids of fluorescence and electron microscopic observations, the ontogenic processes in the fertile and sterile microsporangia are compared, using samples collected from Chitou Experimental Forest and Yeou-Shoei-Keng Clonal Orchard of the National Taiwan University, Nantou, Taiwan. The development of male strobili occurred from August to the end of March. Microsporogenesis starts with the formation of the archesporium and ends with the maturation of 2-celled pollen grains within the dehiscing microsporangium. Before meiosis, there was no significant difference in ultrastructure between the fertile and sterile microsporangia. Asynchronous pollen development with various tetrad forms may occur in the same microsporangium of either fertile or sterile strobili. However, a callose wall was observable in the fertile dyad and tetrad, but not in the sterile one. After dissolution of the callose wall, the fertile microspores were released into the locule, while some sterile microspores still retained as tetrads or dyads with intertwining of exine walls in the proximal faces. As a result, there was no well developed lamellated endexine and no granulate ectexine or intine in the sterile microspores. Eventually, the intracellular structures in sterile microspores were dramatically collapsed before anthesis. The present study shows that the abortion in pollen development is possibly attributed to the absence of the callose wall. The importance of this structure to the male sterility of T. cryptomerioides is discussed.