Carbon Dioxide Exchange During Mist Propagation of Jojoba Cuttings

Abstract

AbstractCarbon dioxide exchange parameters of jojoba (Simmondsia chinensis (Link) Schneider) tip cuttings were studied to determine whether significant photosynthesis occurs prior to rooting, whether fertilization during the rooting process affects carbon dioxide exchange, and whether a non‐destructive method for monitoring progress of root development could be developed. Cuttings were collected from field‐grown plants and placed under intermittent mist in a double‐poly greenhouse. Osmocote (19‐2.6‐l0), a controlled release fertilizer, was incorporated at 0, 1.5, 3.0 and 5.9 kg m−3 into a 1:1 perlite:vermiculite medium at time of inserting cuttings. Photosynthesis and respiration of the cuttings were monitored periodically from the time of insertion until they had rooted and been potted‐up. Gas exchange was monitored at 28°C and at a light level of 700 µmol m−2 s−1. Root respiration was determined using a chamber designed to isolate the base of the cutting together with the medium and any developing roots from the leaves and stem. Significant differences in C02 flux and root growth (dry wt) were found over the 11 wk of the study. Photosynthetic rates during the first wk under mist were moderate (ca. 3 µmol C02 m−2 s−1), declined steadily from the beginning of the study until rooting, and then increased significantly. This suggests that treatments such as shading, which increase plant cutting survival prior to rooting, but which also reduce photosynthesis, could likely be used prior to root formation without negative effects on rooting. Dark respiration declined steadily from the beginning of the study until rooting and increased slightly thereafter. Root respiration paralleled photosynthesis. Photosynthesis at lining out was significantly correlated with root dry weight, root respiration, and leaf succulence. Root dry weight and root respiration were significantly correlated, implying that monitoring of root respiration could be used as a non‐destructive method of monitoring root growth. During the 11 wk of the study, no consistent differences among the fertilizer treatment groups were found in either C02 flux or in root growth (dry wt).