Leaching losses from blueberries grown in sandy soils amended with pine bark.

Leaching of irrigation water from blueberry (Vaccinium spp.) plants intensifies when sandy soils are amended with pine (Pinus spp.) bark. In a greenhouse study, leaching fractions of water (LFW) and nutrients (LFN) were determined from two blueberry (V. corymbosum L.) cultivars, 'Emerald' and 'Jewel', grown in biochar-treated and nontreated sandy subsoil and irrigated with drip emitters using one of three pulse frequencies in a factorial design. The LFW was >50% under Emerald and <20% under Jewel, which has a more extensive root system. When the frequency of same volume of irrigation was increased from 2 (F2) to 10 (F10) pulses per day, the average LFW decreased from 46 to 30%. The LFN from a single fertigation was much lower than the total LFN after 6 d of irrigations applied between two fertigation events. The LFN increased linearly with LFW. Amending subsoil with 2% biochar increased soil pH, limited root growth, and did not reduce nutrient leaching. Eighteen months after plant establishment, 1.9% of applied NO3 --N and 2.5% of applied PO4 3--P from Emerald and 0.8 and 1.0%, respectively, from Jewel leached below the root zone during a fertigation event. During irrigations following a fertigation event, 10.5% of both NO3 --N and PO4 3--P from Emerald and 3.0 and 2.5% from Jewel leached below the root zone. All growth parameters including root/shoot ratio were higher in Jewel than Emerald. This study indicated that leaching rates could be reduced by selecting blueberry cultivars with a dense root system and using a drip irrigation system with >5 pulses d-1 to supply the daily water requirements in pine bark-amended sandy soil.

Can elevated CO(2) improve salt tolerance in olive trees?

We compared growth, leaf gas exchange characteristics, water relations, chlorophyll fluorescence, and Na(+) and Cl(-) concentration of two cultivars ('Koroneiki' and 'Picual') of olive (Olea europaea L.) trees in response to high salinity (NaCl 100mM) and elevated CO(2) (eCO(2)) concentration (700microLL(-1)). The cultivar 'Koroneiki' is considered to be more salt sensitive than the relatively salt-tolerant 'Picual'. After 3 months of treatment, the 9-month-old cuttings of 'Koroneiki' had significantly greater shoot growth, and net CO(2) assimilation (A(CO(2))) at eCO(2) than at ambient CO(2), but this difference disappeared under salt stress. Growth and A(CO(2)) of 'Picual' did not respond to eCO(2) regardless of salinity treatment. Stomatal conductance (g(s)) and leaf transpiration were decreased at eCO(2) such that leaf water use efficiency (WUE) increased in both cultivars regardless of saline treatment. Salt stress increased leaf Na(+) and Cl(-) concentration, reduced growth and leaf osmotic potential, but increased leaf turgor compared with non-salinized control plants of both cultivars. Salinity decreased A(CO(2)), g(s), and WUE, but internal CO(2) concentrations in the mesophyll were not affected. eCO(2) increased the sensitivity of PSII and chlorophyll concentration to salinity. eCO(2) did not affect leaf or root Na(+) or Cl(-) concentrations in salt-tolerant 'Picual', but eCO(2) decreased leaf and root Na(+) concentration and root Cl(-) concentration in the more salt-sensitive 'Koroneiki'. Na(+) and Cl(-) accumulation was associated with the lower water use in 'Koroneiki' but not in 'Picual'. Although eCO(2) increased WUE in salinized leaves and decreased salt ion uptake in the relatively salt-tolerant 'Koroneiki', growth of these young olive trees was not affected by eCO(2).

Cross-correlation patterns of air and soil temperatures, rainfall and Diaprepes abbreviatus root weevil in citrus.

Time series cross-correlation analysis is appropriate when measuring relationships between two different time series. Using this approach, the authors quantified the relationship between the time series air temperature (AT), soil temperature (ST), rainfall, relative humidity (RH) and Diaprepes abbreviatus (L.) (Coleoptera: Curculionidae) root weevil across a period of 30 months, and examined how closely the distribution of Diaprepes root weevil was related to AT, ST, rainfall and RH within this period of time. The study was conducted on a poorly drained Spodosol in a citrus [Citrus sinensis (L.) Osb.] grove in DeSoto County, south-west Florida, from April 2001 to September 2003. Adult weevil populations were monitored using 100 Tedders traps in a 30 x 15 m grid. Weather data (0.6 m AT, 0.1 m ST, 2 m rainfall and 2 m RH) were monitored by Florida Automated Weather Networks. The monthly mean and standard deviation were 22.3 +/- 4.0 degrees C for AT, 24.7 +/- 4.2 degrees C for ST, 146.0 +/- 122.7 mm for rainfall, 78.2 +/- 4.7% for RH and 0.74 +/- 0.59 adults trap(-1) for the root weevil. Weevil density was positively correlated with AT (r = 0.45, P < 0.0133), ST (r = 0.49, P < 0.0067) and rainfall (r = 0.38, P < 0.0450). The environmental variables AT, ST, rainfall and RH were correlated with each other (0.42 < r < 0.99, 0.0246 < P < 0.0001). All weather and Diaprepes variables were autocorrelated with each other within a time of 3 months. The cross-correlation coefficients varied between - 0.59 and 0.65 for the pair-variable between Diaprepes, AT, ST and rainfall, and these pair-variables were correlated across a time period of 4 months. The present results suggested that warm, wet conditions contributed to the root weevil outbreaks, and environmental temperature and rainfall were the variables most closely related to Diaprepes root weevil distribution in time.

Leaf chlorophyll, net gas exchange and chloroplast ultrastructure in citrus leaves of different nitrogen status.

One-year-old 'Cleopatra mandarin' (Citrus reticulata Blanco) seedlings were raised in a greenhouse and fertilized with nitrogen (N) at four application frequencies. Nitrogen-deficient leaves (86 mmol N m-2) had less chlorophyll per unit area, but a greater chlorophyll a:b ratio than N-fertilized leaves (> 187 mmol N m-2). Leaf dry mass per area (DM area-1) and total chlorophyll concentration increased linearly with increasing leaf N, whereas chlorophyll a:b ratio declined. Net assimilation of CO2 (A(CO2)) and leaf water-use efficiency (WUE) reached maximum values in leaves with approximately 187 mmol N m-2. Nitrogen-deficient leaves exhibited small chloroplasts with no starch granules; grana and stroma lamellae that coincided with the accretion of numerous large plastoglobuli in the stroma disintegrated. High-N leaves had large chloroplasts with well-developed grana, stroma lamellae and starch granules that enlarged with increasing N concentration. The lack of an increase in A(CO2) capacity at leaf N concentrations above 187 mmol N m-2 appeared to be correlated with the presence of numerous large starch granules.

Moderate shade can increase net gas exchange and reduce photoinhibition in citrus leaves.

Daily variations in net gas exchange, chlorophyll a fluorescence and water relations of mature, sun-acclimated grapefruit (Citrus paradisi Macfady.) and orange (Citrus sinensis L. Osbeck) leaves were determined in tree canopies either shaded with 50% shade screens or left unshaded (sunlit). Mean daily maximum photosynthetic photon flux density (PPFD) under shade varied from 500 to 700 micromol m-2 s-1 and was sufficient to achieve maximum net CO2 assimilation rates (A CO2). Responses of grapefruit and orange leaves to shading were remarkably similar. At midday, on bright clear days, the temperatures of sunlit leaves were 2-6 degrees C above air temperature and 1-4 degrees C above the temperatures of shaded leaves. Although midday depressions of stomatal conductance (gs) and A CO2 were observed in both sunlit and shaded leaves, shaded leaves had lower leaf-to-air vapor pressure differences (D) along with higher gs, A CO2 and leaf water-use efficiency than sunlit leaves. Estimated stomatal limitation to A CO2 was generally less than 25% and did not differ between shaded and sunlit leaves. Leaf intercellular CO2 partial pressure was not altered by shade treatment and did not change substantially with increasing D. Radiation and high temperature stress-induced non-stomatal limitation to A CO2 in sunlit leaves was greater than 40%. Reversible photoinhibition of photosystem II efficiency was more pronounced in sunlit than in shaded leaves. Thus, non-stomatal factors play a major role in regulating A CO2 of citrus leaves during radiation and high temperature stress.